Boyle Elastic

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The Discovery of Boyk's Law, and the Concept

of the Elasticity of Air in SeventeenthCentury

C. WEBSTER

CommuniCated by J. RAVETZ

IV.V.

VI .VII.

VII ! .

IX.

C o n t e n t s P a g e

I. Introduction . . . . . . . . . . . . ~ . . . . . . . . . . . . . . ". 44t

II . Philosophical Background : The Early Experiment s Concerning Vacua . . 442

IlI . The Torrice!lian Expe rime nt and Its Conflicting Inter preta tions in France, '

1645--t648 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446The "Ela te r" of Air: Jean Pecquet . . . . . . . . . . . . . . . . . 45t

The Introduct ion of Exper iments on Air Pressure into Englan d . : . . • 454

Henry 'Power's Experiments of t653 • • . . . . . . . . . . . . . . . 459

Boyle's First Researches on Air Pressure: The Pneum atic Engine .. .. 464

Power and Towneley: The Direct Measurement of the Elasticity of Air . 470

Power and Towneley: Their Relationship with Boyle and the Ro yal Society 479

X. Boyle's Exper iment s on the Compression and Dilation of Air .. .. .. 484

Conclusions . . . . . . . . . " . . . . . . . . . . . . . . . . . . . . 490

Appendix I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496

Appendix II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

Append i x l I I . . . . . . . . . . . - . . . . . . . . . . . . . . . . . ". 499

Appendix IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500

Appendix V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50t

I. In t roduc t i on

The event s which led to the formu latio n of BOYLE'S Law hav e been described

frequen t ly in his tories of science, and the revolut ionary features Of the Law have

caused i ts widespread use a~ an example in discussions about the n atu re of laws

in Science. However , ther e are notab le deficiencies in our knowled ge of certa in

aspects of the background to BoYLE's work, and i t i s too readi ly assumed that

]3OYLE'S~ ~nterpretati0n oi the Law was similar to the twe nti eth -c ent ury view.

It has long been realised tha t the foun datio n for BOYLE'S work was lai d by

the experiments on air pressure which are popularly connected with TOI~RICELLIand PASCAL. Their work has be en discussed in detail dur ing th e pr esent century ,

and it is now realised that the c0ncept of air pressure was of interest to many

French and I t al ia n natural phi losophers in the mid-seve nteent h century. PASCAL

and TORRICELLI are con seq uen tly reg ard ed as the m aj or con tri but ors to a CO-

Arch. Hist . Exa ct Sci,, Vol. ~ 3 0



442 C. WEBSTER

opera t ive en te rp r i se , in Which the exper imen ta l and theore t ica l work o f the i r

con tem porar ies i s o f the g rea tes t s ign i ficance . 1

Dur ing th i s per iod , cons idera t ion o f the phys ica l p roper t i es o f a a i r wasinseparab le f rom d iscussion o f under ly ing assumpt ions abou t th e phys ica l con-

s t ru c t i o n o f t h e U n i v e r s e an d t h e g en e ra l p r in c i pl e s o p e ra t i v e in n a t u re . E ac h

d ev e l o p m en t i n t h e ex p e r i m en t a l a s p ec t o f t h e s t u d y o f t h e n a t u re o f a i r h ad

a p ro found impac t on ph i losoph ica l d i scuss ions , and the mutua l in te rac t ion be-

tween these tw o aspec t s o f t i le p rob lem had an imp or t an t in f luence on the

even tu a l concep t o f the n a tu re o f a i r. O n ly s lowly d id the e xper im en ta l inves t iga-

t ion become d ivorced f rom i t s ph i losoph ica l o r ig ins .

The in i t i a l impetus o f the Con t inen ta l w ork was l a rge l y lo s t by 1655. B u t

t h e n ew g en e ra t i o n b ro u g h t t h e g ro w t h o f ex p e r i m en t a l s c i en ce i n En g l an d ,

and the s tud ies on a i r p ressu re cu lmina ted wi th the pub l ica t ion o f BOYLE'SLaw i n t 6 6 2 . Th is f i n a l s t age h a s r ece i ved l es s d e t ai l ed t r e a fm en t t h an h a s

the Con t inen ta l work , a l though the con t r ibu t ions o f BOYLE, and his ass is tant ,

HOOI~E, hav e be en de scribe d on m an y occas ions . In th is a r t ic le I wi l l g ive a

more de ta i l ed accou n t o f the Eng l i sh researches than has p rev io us ly been a t~

tem pted , g iv ing par t i cu la r em phas i s to the p rob lems which have been incon-

clus ively considered .

I wi l l beg in by cons ider ing the o r ig ins o f the concep t o f the e las t i c i ty o f

a i r, as d i s t inc t f rom i ts weigh t , by the E ur op ea n inves t iga to rs, du r ing the g rea t

burs t o f exper imen ta l inves t iga t ion which occured be tween 1640 and 1650 , wh ich

resu l ted f rom the rev iva l o f the vacu is t -p len i s t con t roversy . . The in t roduc t ion•o f these exper im en ts in to Eng land wi ll the n be exam ined , fo l lowed by a de ta i l ed

assessme nt of the w ork on air pressure of HENRY POWER and RICHARDTOWNELEY,

who p ioneered the Eng l i sh exper imen ta l s tud ies . F ina l ly , there wi l l be a de ta i l ed

discuss ion o f the r61e of the variou s inve st igator s w ho aided BOYLE in h is search

fo r a quan t i t a t ive express ion o f the e las t i c i ty o f a i r be tween 1658 and 1662 .

I t was in th i s l as t s t age tha t I der ived• mos t benef i t f rom o th er accoun ts , z bu t

i have been ab le to in t roduce supp lemen tary mater ia l , par t i cu la r ly in respec t to

elu cid atin g th e r61es of HE NRY 'PowER an d RICHARD TOWNELEY n BOYLE'S work .

II. Philosophical Background: The Early Experiments Concerning VacuaA t t h e b eg i n n i n g o f t h e s ev en t een t h cen t u ry p h y s i c s w as d o m i n a t ed b y t h e

Ari s to te l i an p r inc ip les as beque a the d .by the neo-scho las ti c ph ilbsophers O the

• . 1 Th e m aj or wo rks dea ling wi th PASCAL an d TORRICELLI nclu de: C. DE WAARD,L'E xpd rien cd Baromdtrique, ses antecedents et ses explication s, Thuars , t936. W.E.KNOWLES MIDDLETON, The Place of Torricelli in t i le History of the Barometer,I s i s , t 963, 45, pp. t 1--28; The His tory o / the Barometer , Lo nd on , 196 4. C. TI~URO.T,Les Exp6riences de Pascal sur le vide et la pesanter de l 'air, Journal de Phy.sique~Ser. 1, t872 , 1, pp. 267 271. P. DUHEM, Le Principe de Pascal, essai historique,Revue Gdndmle des Sciences, t905 , 16, pp. 599 610. F. MATHIEU, P as ca l e t L ' ex -p6rience du Puy de D6me, Revue de Par is , t906, 13, P ar t I, pp. 565 58 9, 772- -794 ;

P ar t h i , pp. 17 9--20 6; 19o7, 14, Pa rt II , pp. 176---224, 367--378, 835--8 76. G. MIHAUD,Pascal e t l 'exp6rience du vide, Revue scienti[ique, Ser. 5, i907 , 7, pp~ 769 77 7.The following accounts are co ncerned with BOYLE'S work b etwee n i660 and

t662, W. S. JAMES,The D iscovery of the Gas Laws; I, Boyle's Law, Science Progress,

1.928, 23, pp. 263--272. D, McKIE, Boyle's La w Endeavouz t948, 7, pp. i48 ~5~.R. G. lXI-.EVILLE, The ~Discovery of Boyle's Law , t66 i-- 166 2, Journa l o / Chemica l

Educat ion , 196 2, 39, pp. 3~6 359.



Boyle's Law and the Elasticity of Air 443

previous half century, 3 and the degree of acceptance (in academic circles a t

least) of hypotheses derived from the growing experimental science was largely

determined b y their consistency with these principles. Thus, the appearance ofexperiments which apparently supported the Democritean notion of vacuum,

caused considerable debate, providing a powerful test of allegiance to the

Aristotelian orthodoxy.

ARISTOTLE4 had elaborately refuted the views of the Democritean atomists,

who had accepted that a space could be completely deprived of body to produce

a macroscopic void, or vacuum coacervatum. They had also argued that motion

could not occur withou t the existence of ,such a vacuum, and t ha t light was a

phenomenon caused by the rapid motion of corpuscles in the void. Expansion

and differences in density were caused by void in its subdivided state, or vacuum

disseminatum, and decrease in density was caused by the increase of the dis-persed vacuum.

ARISTOTLE replied t ha t there was no vo id separate from bodies, and that

there could be no void occupied by any body, or existing in a body. 5 For this

negation of the idea of vacu um he relied upon the concept of "nat ural move ment" ,

believing that a void could not engender the natur al upwar d or downward motion

of simple bodies, or decide their direction or mechanism of propulsion. The

velocity of movement of a body through space was determined by its weight

and the resistance of the medium. Thus a body would pass through a void in-

stantaneous ly, also there would be no difference in the velocit y of a ligl~t and

heavy body in a void.

Neither was the space occupied by a body a void since, even if the body

could be separated, from its attributes, such as heaviness and lightness, it would

still oc cupy the same volume ; thus the suggestion th at a space containing mat ter

was a vacuum was superfluous.

In denying the interstitial vacuum he reached the conclusion that change

of volume occurred by condensation and rarefaction. Thus, when water was

turned into "air", it did not add external matter but the water actualised its

pote ntia lity for becoming air. Change in vo lume was thus~ assimilated into the

category of qualitative changes. He illustrated this by the example of the inter-conversion of air and water, which showed that, by rarefaction and condensation,

the same quantity of matter could alter its bulk.

Similarly the ma tter of a body may also remain identical when it becomes greateror smaller in bulk. This is manifestly the case; for when water is transformed into

- air, the same matter, without taking on anything additional, is transformed fromwhat it was, by passing into the actuality of that which before was only a potentialityto it. And it is just the same when air is transformed into water, the transition beingfrom smaller to greater bulk, and the other from greater to smaller. 6

3 The most notable works written in this tradition were the series of commentaries

published by the Jesuit College of Ciombra; the importance oI the influence of theseWorks in the seventeenth century has been noted by 1~. GILSON,J~tudes sur Le Rdle

de la Pensde Mddidvale clans la ]ormation du sys teme Cartdsien, Paris, 1951.4 ARISTOTLE, Physics, 213 b, 20---214 b 11.5 Ibid., 214b 12- -21 7b 28.

6 Ibid., 217a 26~217a 31. Translation from ARISTOTLE'S Physics, by P.H.WICKSTEAD ~: ~'. M. CORNFORD, London, i929, pp. 36 6-- 369

30*



444 C. WEBSTER:

T h u s t h e e x p a n s i on a n d c o n t r a c t i o n o f m a t t e r i n v o l v e d no b r e a k i n t h e

c o n t i n u i t y o r p l e n u m o f n a tu r e~

T h e A r i s t o t e l i a n e x p l a n a t i o n o f l i g h t a ls o w a s r e l e v a n t t o t h e s e v e n t e e n t hc e n t u ry d i sc u s si o n s of t h e v a c u u m . T h e D e m o c r i t e a n t h e o ry o f l i g h t d i d n o t

p r e c l u d e i ts tr a n s m i s s i o n t h ro u g h a c o m p l e t e l y e m p t y s p ac e , b u t A r i s t o t l e p ro -

p o s e d t h a t l i gh t w a s t h e a c t u a l i s at i o n o f th e p o t e n t i a l l y t r a n s p a r e n t m e d i u m ,

s u c h a s a ir o r w a t e r . T h u s , t h e t r a n s m i s s i o n o f l i g h t r e q u i r e d a c o n t i n u o u s m e d i u m ,

a n d a n y s p a c e l a c k in g t h a t m e d i u m w o u l d b e i n v i si b le . ~

T h e r i v i v a l o f t h e a t o m i s t p h i l o s o p hi e s d u r i n g t h e r e n a i s s a n c e b ro u g h t i n -

c r e a s in g c r i ti c i s m of A r i s t o t e l i a n p l e n i s m , p a r t i c u l a r l y w i t h t h e p o p u l a r i t y o f

LUCRETIUS' De rerum natura, which ha d bee n red i scove red in the f i f t ee r f th cen-

t u r y . I n t e r e s t in a t o m i s m l e d t o t h e i m p o r t a n t I t a l i a n e x p e r i m e n t s w h i ch a t -

t e m p t e d t o p ro d u c e a n a r t i f i c i a l v a c u u m , t h i s d e v e l o p m e n t b e i n g c e r t a i n l ys t i m u l a t e d b y G AL IL EO 'S c o n t e m p l a t i o n o f t h e S c h o l a st i c p r i n c i p l e o f n a t u r e ' s

a b h o r r e n c e o f v a c u u m .

H e c o n c l u d e d t h a t vacuum disseminatum 8 w a s a n e s s e n t i al a s p e c t o f m a t t e r ;

h e p o s s ib l y r e a c h i n g t h i s c o n c l us i o n d u r i n g h i s c o n s i d e r a t i o n o f t h e p ro b l e m o f

t h e c a u s e o f c o h e si o n o f b o d ie s , a n d h e r e i n fo r c ed i t w i t h a n e x p l a n a t i o n o f t h e

p a r a d o x o f t h e rota Aristotdis. H e b e l i e v e d t h a t i t w a s p o s s ib l e to d i s c o v e r a n

inf in i t e nu m be r o f ~vacua wi th in a f in i te space , a nd s ince i t was poss ib le to

d iv ide a l ine by ali. in f in i t e n um be r o f ind iv i s ib le spaces , so i t was poss ib le to

d i v i d e a t h re e -d i n i eh s i o n a l b o d y i n t o a n i n f i n i t y o f a t o m s , i n t e rp o s e d b e t w e e n

a n i n f in i t e n u m b e r o f e m p t y s p a ce s .H ow ever , G A LILEO , l ike DESCARTES, a v o i d e d b u i l d in g a t h e o ry o f m a t t e r o n

t h e a s s u m p t i o n o f a D e m o c r i t e a n v a c u u m . I n a p a s s a g e i n t h e Discorsi h e h i n t e d

t h a t h e w o u l d h a v e d o n e s o i f i t w e re n o t f o r t h e u n a c c e p t a b i l i t y o f t h is h y p o -

t h e s is o n g e n e ra l p h i l o s o p h ic a l g ro u n d s . 9 T h i s w a s w r i t t e n a t a t i m e w h e n D e m o -

c r i t e a n a t o m i s m w a s u n i v e r s a l l y c o n s i d e r e d a t h e i s t i c . T h i s a t t i t u d e w a s o n l y

r e v e r s e d l a t e r i n t h e s e v e n t e e n t h c e n t u r y , a l t h o u g h a t o m i s m h a d b e e n t o l e r a t e d

d u r i n g I s l a m i c ti m e s .

H e b u i l t h i s t h e o ry o f c o h e si o n in b o d i e s ( f o r w h i c h h e h a d g r e a t h o p e s o f

p r a c t i c a l a p p l i c a t io n ) 1° o n t h e a s s u m p t i o n t h a t e v e ry s o r t o f m a t t e r h a d a

chara c te r i s t i c upper , l im i t o f re s i s tance :to rup ture , n He es t i ma ted th i s in the

c a s e o f s o l i d s b y c o m p u t i n g f ro m e x p e r i m e n t a l v a l u e s , t h e h e i g h t o f a c o l u m n

o f t h e s u b s t a n c e w h i c h w o u l d b e o n t h e p o i n t o f b r e a k i n g u n d e r i t s o w n w e i g h t

i f held a t t he top. Cop per yie l ded t he val ue of 4801 Cubi ts . 1~

Liqu ids , inc lud ing wa te r , were cons ide red as bod ies whose cohes ion due to

m i c ro - s t ru c t u r e w a s z e ro , a n d w h o s e b r e a k i n g s t r e n g t h , a s m e a s u re d b y t h e

m a x i m u m h e i gh t o f k c o lu m n , g a v e a t r u e m e a s u r e o f t h e " f o r ce o f t h e v a c u u m " .

7 ARISTOTLE, De Anima, 4 1 8 a 3 1 - - 4 t 8 b t 2 .8 GALILEO, Discorsi e Dimonstrationi Matematiche, intorno h due nuove Scienze,

Leyden, 1638. English translation, Dialogues concerning Two New Sciences, b yH. CREW ~: A. DE S#;LVIO, New York, t914; pp. 20--26.

9 Ibid ., p. 12.10 j. j. FABLE in Studies in the History and Method o[ Science, ed. C. SINGER,

2 vols. , Oxford, 192t ; vol. 2, pp. 207--220.11 GALILEO, 1638, op. c i t . , pp. t6--17.12 Ib id ., p. 17.



Boyle ' s Law and the Elas t ic i ty of Air 445

T h e c r a f t e x p e r i e n c e o f t h e l im i t e d e f f e c ti v e h e ig h t o f l i f t - p u m p s m a y h a v e

he lped h i m tow ards th i s: conc lus ion , bu t such ev idence was con fused and un -

re l iab le , s ince r ea l o r imag inary pumps o f o ther des igns Were in p r inc ip le capab leo f l i f t ing more tha n the 18 cub i t s o f wate r , l a

W o r k in g f r o m th e a b o v e a r g u m e n t , G A LI LE O a s s im i l a t e d t h e p h e n o m e n a o f

pneumat ics to those o f cohes ion in the So l id s ta te , and was consequen t ly led

a w a y f r o m th e e x p l a n a t i o n w h ic h , s o o n a f t e r hi s d e a th , b e c a m e th e m o s t f r u i tf u l

and essen t ia l ly co r rec t one .

H o w e v e r , h e h a d f u l l y e m a n c ip a t e d h im s e l f f ro m th e i d e a of n a tu r e ' s c o m p le t e

a b h o r r e n ce o f v a c u u m , o p e n in g t h e w a y t o t h e e x p e r i m e n t a l p r o d u c t i o n o f

v a c u u m b y s u g g e s t i n g t h a t a c o lu m n o f l i q u id h a d o n ly a lim i t e d r e s i s t a n c e t o

vac uum . In the sam e wor k he con f i rm ed ARISTOTLE'S exp er im en t to show th a t

a i r had w eigh t , conc lud ing th a t wa te r w as 400 t imes as dense as a ir . 1 .GALILEO h a d ce r ta in ly been in f luenced by h is d i scuss ions wi th GIOVANNI

BALIANI ( I 582 - -1666), who was o ne o f the m os t in f luen t ia l I ta l ian p rop onen ts

o f v a c u u m . H e to o h a d r e a c h e d t h e c o n c lu s io n t h a t t h e a tm o s p h e r e e x e r t e d a

p ressu r6 on the e a r th as a r esu l t o f the f a i lu re o f the s ipho n exp er im en t on h igh

h il ls . A s im i la r idea had a l so occu r red to ISAAC BEECKMAN ( t58 8- - t6 37 ) in '

H o l l a n d , w h o e v o lv e d t h e m o d e l o f a i r w h ich w a s s u p p o s e d t o b e l ik e a l a r ge

s p o n g e s u r r o u n d in g t h e e a r th . B y u s in g t h i s a n a lo g y he i n tr o d u c e d t h e v a lu a b l e

c o n c e p t s o f t h e c o m p r e s s ib i l i t y o f t h e l o w e r la y e r s a n d t h e w e ig h t and e l a s t i c i t y

o f the who le mass o f a i r .

I t cann ot be denied th at the lower par t of wate r or a ir is more s trongly compressedthan the upper par t , s ince i t is compressed by i ts own weight , as would happen toan immense sponge, i ts lower par t l? ; ing on the ear th is packed more t ight ly thanthe upper par t . But th is cannot be of great impor tance in the case of a ir which byits na. ture canno t eas i ly be overcompressect and which is -not ver y weighty . Never-theless , i t is necessary to bel ieve that the lower par t is as compressed as i t could be,by the uppe r a ir , and consequently there ex is ts a greater compress ion at i ts base. 15

I t i s p rob ab le tha t BEECKMAN'S the o ry o f a i r p ressu re , a l th ough i t was ex -

p ressed in h i s p r iva te Journal, was i n tro duc ed to h is f r ien d DESCARTEs, who

soon p ropo sed t ha t a i r was ana log ous to a p i le o f woo l f leeces , and th i s s am e

ana lo gy occu r r ing inde pend en t l y to TORRICELLI. Thus I r0 m the inc ep t ion o f thes e v e n t e e n th c e n tu r y i n v e s t i g a t i o n s o f a i r p r e s s u r e , t h e r e a p p e a r e d a m o d e l w h ic h

f a v o u r e d t h e c o n c e p t o f t h e e l a s t i c i t y o f a i r .

Soon af ter the publicat ion of GALILEO'S Discorsi in 1638, the I ta l ian in-

v e s t i g a to r s t u r n e d t h e i r a t t e n t i o n t o t h e e x p e r im e n ta l p r o d u c t io n o f a v a c u u m .

T h e f i rs t s u c c e ss f ul a p p a r a tu s w a s p r o b a b ly : d e v i s e d b y G AS l'A RO BE RT I (b . t 6 . .

d . 1643 ?) in R ome , t he expe r im en t be ing per fo rm ed by h im an d h is d i s t ingu ished

co l lab o ra to r s befo re t642. I6 The ap pa ra t us was a long g lass, tube , exp and ed in to

a smal l g lobe a t the upper end , and the open ings a t e i ther end cou ld be c lo sed

b y b rass sc rews . T h e t .ube was p r oba b ly abo u t 33 f ee t long . The Whole tube

was f i l l ed wi th wate r and the lower end immersed in a tub o f the same l iqu id .

i8 C. DE WAARD, 1936, op. cit., pp. 73~-74.14 GALILEO, 1638 , op. cit,, pp. 79- -80 .la ISAAC BEECKMAI'{ Journal, 24 December t6 20 - - !9 Feb ruary , 1621 , quo ted

from C.DE WAARD, 1936, Op. cit . , ip p. 155--156. Tra nsla ted from t he French.16 Ibid., 101 --t0 9. - - W. E. KNOWLES MIDDLETON, 1963,-op. cit., pp. 14- ~6.



446 C. WEBSTER:

Upo n the lower t ap be ing opened ; the w ater descended- f rom the g lobe , to s tan d

i n t h e t u b e a t ab o u t t 8 cu b i ts o v e r t h e s u r f ace o f t h e w a t e r i n t h e t u b .

Th e ex p e r i m en t w as p e r fo rm e d p r i v a t e l y , an d p u b l ica t i o ns r e l a t i n g t o i t w e rede layed and con t rad ic to ry . Also , as an exper imen t conce ived as a la experimentum

crucis between p len i s t s and vacu is t s i t showed many confus ing fea tu res , char -

ac te r i s t i c o f a f i r s t t r i a l . The Supposed vacuum in the g lobe t ransmi t ted l igh t ,

m ag n e t i s m an d s o u n d ( t h i s l a s t b ecau s e o f co n d u c t i o n b y t h e w o o d en f r am e

suppor t ing the be ll ). Moreover , s t range sounds .were hea rd as the l iqu id descended

(which were due to the re lease o f d i s so lved a i r) . Also the he igh t o f the w ate r

changed overn igh t .

Fur ther , the ques t ion o f Dem ocr i tea n a tom ism was , a t th i s time, " as de l ica te

as tha t o f the Copern ican hypo thes i s , and . th is d i scouraged d i scussion and pub l ica-

' t i o n o f t h e ex p e r i m en t .

IiI. The Torricellian Expe riment and Its Conflicting Interpretations in France,

1645 1648

In tw o let ter s of Jun e, t64 4, EVANGELISTA TORRICELLI (t60 8 1647) z7 pro-

posed a more e legan t fo rm o f th i s exper ime n t , u s ing me rcu ry and a tu be on ly

thre e feet long. Th e e xp eri me nt v /as perfo rm ed fo r h im by V!NCENZO VIVlANI

( t 6 2 2 ~ 1 7 0 3 ) , an d i t w as fo u n d t h a t t h e m er cu ry w as s u p p o r t ed t o a h e i g h t

o f 29 inches . Fu r ther , he had des igned th i s exper imen t to t es t the "ocean o f a i r"

h y p o t h esi s , p r ed i c t i n g t h a t u n d e r t h is h y p o t h es i s , w a t e r w o u l d b e s u p p o r t ed t o ahe igh t o f 32 fee t . He ha d r/o inh ib i t ions abou t a dop t ing the concep t o f vac uum ; the

absence o f mat te r in the space above the merc ury cou ld be~shown by rep lac ing

t h e m ercu ry b y w a t e r , w h i ch co m p l e t e l y f il led t h e t u b e .

TORRI~ELLI'S work thus as s imi la ted the var ious f ra gm en t ary ideas and ex -

p e r i m e n t s o f h i s co n t em p o ra r i e s i n t o a h y p o t h e t i co -d ed u c t i v e f r am ew o rk , an d

his , letters, which were addressed to MICHELANGELOR l C C I ( t 6 t 9 - - t 6 8 2 ) , b ecam e

t h e e f f ec t i ve p ro p ag a t o r s o f t h e co n cep t s o f v acu u m an d t h e w e i g h t o f a i r , .

the con t r ibu t ion s o f BERTI and h i s co l labora to rs in Ro me be ing over looked .

R lc cI was in co nta ct wi th MARIN MERSENNE (t 586----t648) of Pa ris , wh o was

Europe ' s l ead ing pub l ic i s t o f sc ien t i f i c in fo rmat ion , and i t was in the moret o l e r an t a t m o s p h e re o f F ran ce t h a t t h e u n o r t h o d o x i c! ea o f v acu t l m w as s u b j ec t ed

to de ta i l ed sc ru t iny .

In 1644, RICCI sen t MERSENNE ex tra cts of TORRICELLI'S lette rs, bu t th er e

was l i t t l e p rac t ica l response in France un t i l a f te r MERSENNE had v i s i t ed I t aby

in 1644 and t645.18 In t645, he v is i ted Florence and at tended a demonstrat ion

o f t h e ex p e r i m en t , an d d u r i n g h is s t a y i n F l o ren ce an d R o m e h e h ad s c ien ti f ic

d i scuss ions wi th the majo r par t i c ipan ts in the I t a l i an researches .

17 EVANGE LiSTA TORRICELLI,the le t te rs were wr i t t en on l l t h and 28 th June ,

1644, but they were not published until 1663; CARLO DATI, L'ettera a Filaleti diTimauro Antiate de la vera storia della Cicloide /amosissima esperienza del!'argento

vivo, Florence, 1663; also in Opere di Torricelli, ed. G~ LORIA & G. VA~SURA, vo1. 3,t 919, pp. t 897-190, 198 --2 0t. Eng lish tra nsla tion in The Physical Treatises o/Pascal,ed. J. H . B. SPIERS ~¢ A. G. U. SPIERS, New York;, '1937, pp. 16 3-- t70 .

18 C. DE x~VAARD, 1936, o p . cir., pp. !17-~-119. P. LENOBLE, Mersenne, ou la

naissance du mdcanisme, Paris, 1943, pp. i 18 -- t 19.



Boyle 's Law and the Elas t ic i ty of Air 447

U p o n h i s r e t u rn t o F ran ce i n March , t 6 4 5 , h e p u b l i c i s ed i n fo rm a t i o n ab o u t

' roRRICELLI'S experiment , whi le los ing s ight of the contr ibut ions of BERTI and

o the r I ta l i ans . S ince the course o f the ensu ing expe r imen ts in Fr an ce has beenw e l l d o cu m e n t ed , I w i ll co n cen t r a t e o n t h e g ro w t h o f t h e i d ea o f t h e e l a s t ic i t y

of air.

The T orr ice l l i an expe r im en t was f i r s t per fo rm ed in Fran ce by PIERRE PETIT

( t589-- t677) , the eng ineer in c harge o f the fo r t i f i ca t ions a t Rouen . 19 Th is w a s

a t R o u e n i n O c to b e r , t6 4 6. I t m a rk ed t h e i n cep t i o n o f an i n t en s iv e s e ri es o f

i n v es t i g a t i o n s o f t h e p h y s i ca l p ro p e r t i e s o f a ir , w h i ch p ro v i d e s o n e o f t h e

p i o n ee r ex am p l e s o f t h e co l l ab o ra t i v e ap p ro ach t o ex p e r i m en t a l r e s ea rch an d

w h i ch w as s y m p t o m a t i c o f t h e t r en d w h i ch re s u l t ed i n t h e fo u n d a t i o n o f t h e

sc ien t i f i c academies in th i s cen tu ry .

Al thou gh the Fre nch exper imen ts a re usua l ly as soc ia ted w i th BLAISE PASCAL(t623--1662 ) and h i s b ro ther - in - law, FLORIN PERRIER, an imp or tan t par t was

a l so p layed by MERSENNE, ETIENI~E NO]~La n d ROBERVAL,whi le con t r ibu t ions

w ere m ad e b y A D R IEN AUZOULT,PETIT, JACQUES PIERIUS, JEAN PECQUET, asi

well as DESCARTESand GASSENDI who u t i l i zed the exper imen ta l ev idence in

the i r r iva l ph i losoph ies o f na tu re . Through MERSENNE, he d i scuss ions were

ca r r i ed f a r a f ie ld , t o En g l an d , H o l l an d , I t a l y an d P o l an d .

Th e i n i t ia l F ren ch e x p e r i m en t s w e re co n ce rn ed w i t h t h e r ep e t i t i o n o f TOR RI-

CELLI'S w0rk and the ver i f i ca t ion o f the hypo thes i s o f the weigh t 0 f a ir . In 1647

PAscal . con fi rm ed TORRICELLI'S pre dict i on b y sh owing th at a i r su.p p o r t e d a

33 foot colu mn of wa ter or wine, S° and MERSENNE com pa red the densi t ies ofwa ter and air , conclu ding tha t Water was 1 ,356 t ime s as dense as a i r . 21

Th e re w as f a r l e ss ag reem en t o v e r t h e i n t e rp re t a t i o n o f t h e s p ace ab o v e t h e

m er cu ry o r " ap p a re n t v acu u m " , i n v i ew o f t h e p o w er fu l A r i s t o t e ti an a rg u m en t s

aga inst abs olu te v oid. In 164"7, ev en PASCALwas u n w i l l i n g t o ad o p t t h e v acu u m

t h e o r y , a l t h o u g h h e n o t e d t h a t t h e " e x p e r i m e n t a l a n d D e m o c r i t e a n " v a c u a h a d

many fea tu res in common, bu t aga ins t these S imi la r i t i es he p laced the t rad i t iona l

a rg u m en t s ag a i n s t v acu u m .

MERSENNE, ~ h o was o therw ise one of ARISTOTLE'S mo st s t r in gen t cr i t ics a lso

b ecam e i n c rea s i n gl y d o u b t fu l ab o u t t h e i d ea o f v acu u m , d u r i n g t 6 4 7 a n d t 6 4 8 .

Th e o p p o s it i o n t o t h e i d ea o f v acu u m cam e f ro m t w o d i s t i n c t q u a r t e r s ,

the one p roposed tha t the space Was f i l l ed by a materia subtilis o r a e t h e r , t h e

o t h e r , t h a t i t w as f i l l ed w i t h r a r e f i ed ai r. Th e fo rm er v i ew w as ad o p t ed b y

DESCARTES and ETIENNE NOEL, an d i t w as w idely inf luent ial in En gla nd upo n

such d iverse au thors as HENRY MORE, POWER,and NEWTON, DESCARTESa n d

NOi~L p roposed t ha t the d escen t o f merc ury was assoc ia ted wi th t i l e en t ry o f

a sub t le m at t e r in to the space , wh ich passed e i ther f rom t i le wall s o f the tube ,

x9 CI DE WAARD, t9 36 oP. ci r., p. 1t9 . ~ P. PETIT,Observation touchant Ie Vuide/aite pour la premier Fois en France contenue en une lettm dc~ite ~ Monsieur Chanut

Resident poffr sa Ma]estd en Suede, par Monsieur Petit, Intendant des [,orti/ications,le 10 novembre 1646, Paris, t647. This is given in Oeuvres de Blqise Pascal, ed. L..BRUNSCHWIG & P. BOUTROUX,Paris, 1904--t914; voh t , pp. 329--345.

20 BLAISE PASCAL, JExperiences Nouveltes touehant le Vuide, Paris, !647; O~uvres

op. ct., vol. II,, pp. 74__76.*x MARIN MERSENNE, Cogitata Physico-Mathematica, Paris, 1644. "De Hydraulicis

et Pneumaticis phenomenonis" , Proposi t io XXIX.



448 C. WEBSTER

o r t h r o u g h th e ~ m e r c u r y . T o t h e m th e i d e a o f v a c u u m w a s p h ilo s o p h ic a ll y i n -

admiss ib le s ince ex tens ion wa s a defin ing p ro per ty o f ma t te r .

T h e r e w a s h o w e v e r t h e s e c on d , m o r e p o p u la r e x p l a n a t i o n O f t h e s p a ce , w h ic hw a s m o r e s t r i c t l y i n a c c o ~ l w i th A r i sto t e l ia n p h y si c s , i t p r o p o s e d t h a t t h e s p a c e

was a man i fes ta t ion o f the g rea t powers o f expans i on o r r a re fac t ion o f a i r , when

r e l e a se d f r o m th e c o m p r e s s io n of t h e u p p e r l a y e r s o f t h e a tm o s p h e r e . T h i s t h e o r y

h a d t h e tw in a d v a n ta g e s o f c o n f o r m i ty w i th A r i s to t e l i a n p rin c ip l e s a n d a b u n d a n t

e x p e r im e n ta l e v id en c e . T h e i de a l os t g r o u n d o n ly s lo w ly a l t h o u g h i t w a s o p p o s e d

b y GASSENDI an d DESCARTES alike, its influen ce be ing no tic eab le in HOBBES'

cr i t ic isms of BOYLE.

Alre ady by t644 , MERSENNE had co l lec ted toge ther exam ples o f the g rea t

powers o f r a r e fa c t ion and condensa t ion o f a ir , in the cou r se o f wh ich he es t i ma ted

th e d e n s i t y o f a i r r e l a t i v e t o w a te r . H e s h o w e d th a t a i r c o u ld b e r e v e r s ib ly

condensed to o ccu py t /1000 th par t o f i t s fo rm er vo lume. 2~

D u r in g t h e c o u r s e o f h i s d e v e lo p m e n t o f t h e a e th e r h y p o th e s i s , ]~TIENNE

NOi~L, who ha d bee n DESCARTES' tea che r a t La Fl&che, foun d t ha t the in tro -

duc t ion o f a smal l vo lume o f a i r caused a g rea te r r educ t ion~ i~ l the mercu ry leve l

t h a n t h e s a m e v o lu m e o f w a te r , w h e n in t ro d u c e d a b o v e t h e m e r c u r y in t h e

Tor r iceUian experimer~t , za Th is was a p arado x ica l r esu l t, s ince w ate r was a t l eas t

4 00 t im e s a s d e n s e a s a i r. T h e d e p re s s io n o f t h e m e r c u r y l e v e l w a s t h e r e f o r e

no t a man i fe s ta t ion o f weigh t a lone . No i~ l. exp la in ed the p ara dox b y p ropos ing

th a t t h e d e p r e s s ion i n le v e l w a s c a u s e d b y t h e a e th e r , w h ic h w a s p r e s e n t t o amu ch g rea te r ex te n t in a i r tha n in wate r . Howe ver , the s ign i ficance o f th i s

e x p e r im e n t w a s n o t i n i t s c o nc lus io n , w h ic h, l i ke o th e r a e th e r e x p l a n a t i o n s w a s

a p rob le m o f specu la t ive r a th er t ha n e xper i me n ta l phys ics , bu t in pI6"v iding the

b a s i s f o r q u a n t i t a t i v e m e th o d s o f m e a s u r in g t h e d e g re e o f e x p a n s io n o f a v o lu m e

o f a i r . T h i s m o d i f i c a t i o n o f t h e T o r r i c e l l i a n e x p e r im e n t c o u ld b e a d a p t e d t o

measu re the behav iou r o f a i r under e i ther increased o r decreased p ressu re .

This sa me ex pe r im en t h ad bee n e vo lve d also by GILES PERSONE DE ROBERVAL

( t602 t675 ), who was p ro fesso r o f ma the ma t ic s a t the Col l~ge Ro yale in Par i s ,

a n d w h o w a s o n e o f "DESCARTES' most per s i s ten t c r i t i cs . He was one o f the

p r o m in e n t v i r t u o s i o f t h e p e r io d , w h o h a d e x p lo r e d n u m e r o u s m a th e m a t i c a l a n dphys ica l p rob lem s . He was a f r iend o f bo th MERSEN~E and PASCAL and took

pa r t in the r e gu la r - sc ie n t i f ic m ee t ing s in Pari s . H is wr i t ings on a ir p ressu re

be t r a y s imi la r i t ies w i th PASCAL'S . He had a pos i t iv i s t b ias , and he was un -

wi l l ing to dec la re in f avour o f e i ther the p len is t o r vacu is t schoo ls l Fu r thermore ,

h e h a d g r e a t i n g e n u i ty i n d e v i s in g 'e x p e r im e n t s , w h ic h w e r e s c r u pu lo u s ly d e s c r ibe d

a n d e x p l a in e d . A s w i th PASCAL,h i s w o r k w a s k n o w n m o r e t h r o u g h th e i n f o r m a l

d e m o n s t r a t i o n s a n d d i sc u ss ion s o f t h e e x p e r im e n t s t h a n b y p u b l i c a t i o n , f o r h i s

w r i t in g s o n a i r p re s s u re h a v e n o t b e e n p u b l i s h e d u n t i l t h e p r e s e n t c e n tu r y . H i s '

in f luenc e was m an i fe s t p r ima r i ly in the wr i t ings o f MERSENNE and PECQUET.

ROBERVAL'S f i r s t e x p e r im e n t s o n a i r p r e s s u r e w e r e p r o m p te d b y t h e d i s -

ag ree me n ts ov er PETIT 'S v ind ica t i9 r r o f the v acu is t i n te r p re t a t ion o f the T or r ice l l -

~ Ib id . , Proposi t io XXIX.2a ]~-TIENNENO~L,Gravitatis comparata, seu comparatio gravitatis aeris cure h ydrar-

gyri gravitate, Pari s, t648. pp. 55 56.



Boyle's Law and the Elasticity f Air 449

fan experiment. 2~ JACQUES PIERIUS gave a scholas tic rep ly to the Torricelli an

theory, proposing that natur e's abhorrence of vacu um was limited an d th at tile

apparent vacua• were filled by the vapour of the liquid in the tube. During hisexamination of the Torricellian experiment, ROBERVAL nfiltrated bubbles of air

and water into the apparent vacuum, andP F I

concluded that bubbles of air did not pass

into the vacuum, but remained above the

mer cur y as d istinct bubbles. 25

But, during the next year, he reversed

these opinions and evolved an elaborate

theory to explain that the space contained

rarefied air, an explanation that he found

accorded well with his mechanical princi-ples, as well as disarming the peripatetic

opponents of va cuum . ~6

T h i s change of opinion was induced

by the experiments which illustrated air's

great powers of expansion, the most perti-

nent e xper imen t being the carp-bladde r

experimen t, which he devised himself. 27

The swim-bladder was removed from a.

carp, and the air pressed out; the neck

of the bladder was then tightly ±ied, and

it was placed at the apex of a Torricellian

tube: The tube was filled with mercury,

immersed into a dish of mercury, and

when the mer cur y fell, the bladde r was }

suspended in the vacuum. The bladder

now inflated. This experiment was visually

impressive and its popular ity proba bly ex- Yeeded that of the Torricellian experiment

itself, until it became ~n indispensible Fig. t . JEAN PECQUET,Experime~itc* No va Anatomica,

pa rt of fu tu re works on air pressure. In te rest Pa~i~, 65t, Plate I. T~e ca~p bladder ~p~r~,,t

in this experiment was greatly enhanced

by its use to criticise DESCARTES' aether hyp9thesis. ROBERVAL proposed tha t,

under normal circumstances air is compressed or condensed ( c o m p r e m e n t u s e u

~4 G. P. D~ ROBERVAL, "de Vacuo nar rat io Ae. P. de Roberval ad nobilissimumvirum DI de Noyers, 20 Sept., t647." See PASCAL'SOeuvres op. cit., vol. II, pp. 21--35.JACQUES PIERIUS published his detailed criticism of the vacuist t heory in i648~Jacobi PierS, doctoris me dic s et .phli losophiae pro/essoris , A d expe ¢im entia m circa

vacuu m IP. P. Valer ians Ma gn i demonstrat ionem occulamm et mathem at icorum quo-

rumdam nova cogi ta ta , Respons io ex Pe~, ipate t icae Pr incip i i s desumpta , Paris, 1648.

25 G. P. DE ROBERVAL, i647, op. cir., pp. 26--2.7.26 ]i{OBERVAL expressed his change of mind in a further letter to DES NOYERS,

which was written in May/June, 1648. Like the former letter it was not publisheduntil the present century. "A. P. de RoBerval de Vaeuo Narratio ad Nobilem virumdominum des Noyers," Pascal's Oeuvres, op. cir., vol. II, pp. 310--340.

27 Ibid., pp. 325--328. A trans lation of the whole bf the carp-bladder experimentis given as Appendix I. See footnote 177 and Illustration i.



450 C. WEBSTER:

condensant is ) b y th e u p p e r l a y e r s a n d t h a t i t h a s a n a tu r a l p o w e r o f r e si li e nc e

(res i l iendum [acul tas) w h ic h e n a b l e s i t t o e x p a n d w h e n r e l e a s e d f r o m c o m p r e s s io n .

Such a c i r cum stanc e occu r red in the b ladder , w h ich , a l thoug h la rge ly def la ted ,s t i ll had a l it t l e r es id ua l a i r ; wh en th i s a i r was p laced in the r edu ced p ressu re

o f t h e v a c u u m , it e x p a n d e d u n t i l i t s f o rc e w a s e q u a l l e d b y t h e t e n s io n o f t h e

e las t ic b ladder .

PASCAL had a l so no te d the exp ans ion o f a i r when sub jec ted to r edu ced p res -

su re, w l~en he no te d th e increase in vo lum e o f a par t ia l ly in f la ted b ladd er w hen

carr ied up a h i l l .

H en ce if a bal loon, only half inf la ted : - no t fu l ly so , as the y general ly are - -were car r ied up a mountain , i t would necessar i ly be more inf la ted at the mountaintop, and would e xpa nd in the degree to which it w as less burdened. 28

T h u s a l r e a d y PA SCAL h a d s p e c u l a t e d t h a t t h e r e w a s a s im p le r e l a t i o n s h ip

' b e tw e e n th e v o lu m e o f a i r a n d t h e e x t e r n a l p r e s s u r e o n i t, a l t h o u g h th i s w a s

"n o t a n e x p re s s io n o f t h e p r o p o r t i o n a l i t y b e tw e e n a tm o s p h e r i c p r e ss u r e, a n d t h e

e x p a n s i o n o f t h e a ir . ROBERVAL a lso came to th i s conc lus ion in a fu r ther

expe r ime n t , wh ich i s quo te d as Appen d ix I I . L ike N0 i~L, ROBERVAL in t ro -

d u c e d e q u a l v o lu m e s o f a i r a n d w a te r a b o v e t h e m e r c u r y i n t h e T o r r ic e l l ia n

e x p e r im e n t , a n d n o t e d t h a t a i r c a u s e d t he g r e a t e r d e p r e s s io n o f t h e m e r c u r y

l e v e l . T h i s c o u ld b e e x p l a in e d i n a s im i l a r m a n n e r t o t h e c a r p - b l a d d e r

e x p e r im e n t w a te r p r e s s e d o n t h e m e r c u r y b y i t s w e ig h t, w hi le a ir e x e r t e d a

fo rce o f d i la ta t ion (v i aut appe t i tum ad rare/act ionem). F u r t h e r , h e n o t e d t h a t

a v o lu m e o f a i r c a u s e d t h e g r e a t e s t d e p r e s sio n o f m e r c u r y i n s m a l l e r t u b e s a n d

th e l e a s t e x p a n s io n i n l o n g e r tu b e s . T o e x p l a in t h i s h e a s s u m e d th a t a i r ' s s p r in g -

l ike p roper{y was s imi la r to the r es i l ience o f a bow, wh ich , when r e leased f rom

c o n s t r a in t , h a d t h e g r e a t e s t r e b ou I~ d a t t h e b e g in n in g o f it s s p r in g a n d t h i s

d imin ished un t i l i t r e tu rned to qu iescence . 'L ikewise , a i r had the g rea tes t power

o f' sp r ing a t the beg inn ing o f i t s expans ion , w hen i t was ju s t r e leased f rom com-

p r e ss io n o f t h e w h o le w e ig h t o f t h e a tm o s p h e r e . T h i s f o rc e t h e n r e l a x e d a s i t

e x p a n d e d . T h u s i n a l o n g t u b e t h e m e r c u r y w a s d e p r e s s e d s l i g h t l y b y a i r i n i t s

e x p a n d e d a n d w e a k s t a t e .

Ac in it io quidem su ae rarefact ionis magnis v ir ibus raref i t , qu ia magnis , pu tato t ius e lementar is naturae prementis v ir ibus cond6nsabutur . Inde vero sensim lan-guescunt ips ius v ires , qu ia minus ac minus premitur a tque condensatur ~ . .29

Th is passage i s r emin iscen t o f ]30YLE'Sc o n c lu s io n t h a t h is h y p o th e s i s e x p l a in e d

"h ow m uc h-a i r d i la ted i t se l f lo ses o f i t s e las t ica l fo rce" . 80

ROBERVAL'S 'aCcoun t showed a g rea te r c apa c i ty o f r educ ing th i s exp er im en t

to t h e f o r m o f a p r o b l e m in m e c h a n ic s t h a n d id o th e r F r e n c h a u th o r s . H e h a d

c l e a r ly i n hi s m in d t h e i d e a t h a t t h e e x p e r im e n t r e p r e s e n t e d a n e q u i l i b riu m

b e tw e e n th e p r e s s u r e of t h e a tm o s p h e r e o n t h e o n e h a n d , a n d t h e p r e s s ur e o f

2s BLAISE PASCAL,Tra itez de l'J~quilibre des liqueurs, et de la Pe san teu r de la Mass ede i'air, Paris, t663. English translation, op. cir. (note t7), PP. t ~ 7 5 ; this quot atio nis taken from p. 30.

29 G. P. DE t{OBERVAL, t648, op. cit., p. 316.so :ROBERTBOYLE, New Experiments Physico-Mechanieal, Second edition Oxford,

1662; The Works o] the Honourable Robert Boyle, ed. T . BIRCH, Lo ndo n, t 744; vo l. 1,p. 1o2.



]3oyle's Law and the Elasticity of Air 45t

the column of merc ury and enclosed air on the other. An y disturbance of this

equilibrium by altering the volume of air in the tube, caused a readjustment of

the mercury level to restore the equilibrium. This principle of conservation, hesubsumed und er his general principle that gra vity was due to the m utua l attrao~

tion of the ultimate parts of nature:

si respexerit ad vim illam qua partes totius naturae elementaris invicem com=primuntur ad unicum systema elementare constitutendium: sl

ROBERVAL'S experiments and theories a ttr act ed great atte ntion in Paris, and

on 5th May, 1648, PECQUETwrote to ]ViERSENNE:

Monsieur de Roberval performed marvels here, and yesterday he performed suc-cessfully the experiment with the carp' s bladder; he had a great number of c~bservers.3~

~-VIERSENNE,like many other French natural philosophers, was impressed by

ROBERVAL'S work, and he disseminated information abou~ the rarefaction of

air to his European correspondents. He now hesitated over the vacuist inter-

pretation of the Torricellian experiment, expressing these doubts in his R e-

/ lexiones Phys ico-mathemat ica of t647.

In his last work, the new preface to the H ar m on ic or um L i br i X I I , he included

an account of the depression of mercury by a volume of air, and in a letter to

HEVELIUS in June, 1648 33 he noted th at the ques tion of va cu um had been

reopened, b ut expressed his res erva tions about the Aristotelian the ory of rare-

faction. However, by July, t648, he was convinced tha t the space contained

rarefied air.We see that numerous tracts are written in Poland on the vacuum in the glass

tube, but nothing comes of it, and similarly in our experiments, of which even nowwe are multiplying new ones, but nevertheless we conclude that it is rarefied air,not vacuum, a4

This ma y be t aken as MERSENNE'S final stat emen t about the Torricellian

experiment, si~ae he died on 1st. September, t648.

IV. The "Elater" of Air: Jean.Pecquet

Another author who was impressed by ROBERVAL'S heory of the spontaneous

rarefaction of air was JEAN PECQtlET (1622 1674). He has a n assured place in

the h istory of science throug h his discovery of the chyle receptacle and the th oracic

duct of the lymphatic system, which was made during his demonstration of

ASELLI'S chyle vessels in dogs at Montpellier, when he was a s tuden t of medicine

at th at University. His stud y of the lymp hatic sys tem was one of the most signi-

ficant contributions to experimental physi ology since HARVEY'S discovery of

circu lation ; PECQUETdefended HARVEY'S work again st JEAN RIOLAN, of ParAs,

who was the most influential opponent of the idea of circulation. PECQUET nte-

Zl G. P. DE ROBERVAL, 1648, op. cir., p. 3 t 7. This same principle had been stressed

in his previous work, Aristarchi Samii de Mundi Systemate Libellus, Paris, 1644, p. 4.3* PECQUET'S letter is translated from the quotation in PASCAL'SOeuvres, vol. II,

p. 295.a3 M. MERSENNE, letter to HEVELIUS, t June 1648; PAscAL's Oeuvres ;col. I I ,

pp. 302 303.~4 M. MERS2ENNE, letter to HEVELIUS, 27 July 1648; PASCAL'SOeuvres vol. II,

p. 309.



452 C. WEBSTER:

grated the theory of the mction of chyle into the general theory of circulation.

His discoveries were made in t647, and h e gathe red various short ess ays on

physio logy into a small volume,E x p e r i m e n t a N o v a X n a t o m i ca ,

which was publish-ed in t651. 3~ This, his first work, became very• popular a nd it passed th rough

many editions, being translated into English in 1653. This is significant, since

only the most influential_ anatomi cal works were tr ansla ted at this time.

This book is important for the purposes of this article since it contained a

section on experiments on air pressure, which would thus b e distr ibute d to a

wide audience, by virtue of their association v)ith the physiological work. Thus

paradoxically ; a physiological treatise became one of the most accessible and

widely read accounts of the French experiments on air pressure.

It has been no ted that PECQUET report ed • ROBERVAL'S carp-b ladder experi-

ment to MERSENNE in i647. I n the next yea r he was writing a further ac coun tof an experiment on air pressure. At the same time he was attracted to attend

the weekly, scientific meetings in MONTMOR'Shouse in Paris, and it m ay be assumed

that the theories of air pressure were of great interest to him at this time. It is

therefore not unnatural that he should include an account of air pressure in his

first book. Unfo rtunately , the great acuteness of PECQUET'S intellect, shown i n

these initial physiological and physical studies, was soon clouded by an addic-

tion to alcohol.

The purpose of the section on air pressure was appare nt from the', first chap ter

heading:

Esse non PONDUS tantum, sed rareiactarium Aeri ELATEREM Experimentisdemonstratur. 36

PECQUE.T collected toge the r various experiments which illu stra ted that air

had not only weight but also a spring or elater. The originality of the work was

therefore not in the introduction of new experiments, for all the experiments

we re from other, albeit unpublished, sources. He described the P u y de D6me

experiment of PASCAL and PERIER, 87 and it was th ro ugh PECQUET'S account,

rat her than PASCAL'S that this experiment was intr oduced to POWER, BOYLE

and SINCLAIR in Englar ld a nd Scotland . He gave also AUZOULT'S modi fica tion

of PASCAL'S va cuum in the vacuum exper iment. 38 Fr om ROBERVAL he too k the

carp-bladder experiment and the experiment of enclosing air or water above the

mercury of the Torricellian apparatus. This experiment is quoted in full as

Appendix I I I (see also Illu strati on 3) ; and it indicates the terse Style which was

85 JEAN PECQUET, E x p e r i m e n t a N o v a A n a t o m i c a , Paris, 165t, 4 °. There was.an-other issue published in Paris in the same year; E x p e r i m e n t a N o v a A n a t o m i c a . . .

Hardev i c i apud J . To ll i um, ]ux ta exemplar P ar i s i i s impres sum, t2 °. - - A secondedition appeared in Paris in 1654. The English edition was produced in conjunctionwith THOMAS BARTHOLIN'S ract on the lymphatic system; N e w A n a t o m i c a l E x -

per iments o / J . Pecquet . . . Also an anatomical d isserta t ion o[ the movemen t o / bloodand chyle . . . b y T . Bar thol inus , 2 vols., London, t653, t20 . -- HENRY POWER!S

• ibrary had both the English and the 1651 edition of this work. - - My referencesare to the most widely available edition, Joann i s Pecque ti D iepae i Exper imen ta Nova

Anatom ica, Quibus In c@ ni t um hactenus Chyl i Reeeptaculum, & ab eo pe~:-Thoraeem

in ramos usque Subclavios Vasa Lactea de teguntur . . . . Amsterdam, 1661, 1.6°.a2 Ibid. , p. 87.av Ibid., pp. 99 ~t 0 t.as Ibid., pp. 102--106; see Illustration 2.



Boyle's Law and the Elasticity of Air 453

adopted for thes~ experiments, which contrasts strongly with complex ramifica-

tions of R O B E R V A L ' S arguments.

The importance of PECQUET'S work lies therefore in its effective publicityof the French experiments and in its stress on the property of the elasticity of

air. Further, he adopted the terminology to describe this phenomenon which

has become integrated into the English language.

F II F I f !

F

G

Fig. 2. JEAN PECQUET,Experimenta Nova Anatomica,Paris,162t, Pla te I I. AUZOULT'Svacuum-in-vacuum experiment.The upper tube is shown incompletely and is sawn off

a t F. The containers C ~nd D hold mercury

Fig~ 3. JEAN PECQUET,Experimenta Nova Amztomica,Paris,165t, Plate IU . PECQUET'Sdemonstration that air exertspressure by virtue of its elasticity, while water exertspressure by its weight. Equal volumes of water (E) and air(B) are placed above mercury (AE) in a Torricellian tube

ROBERVAL had maintained the Aristotelian terminology in explaining the

expansion of air, although he inferred that the condensation and rarefaction

was a "spontaneous" or active property. It was perhaps his deference to the

plenist theory which prevented him from expressing a physical model to explain

this property. PECQUET no w adopted the terms "elate r" and "elastic" to describe

the same phenomenon. Neitherlcerm had been used in classical Latin, and P E C Q U E T

took them from the Greek noun ~aT~ (elaterl that which or one who drives).

This term was widely adopted by English authors, and through the works o~

C H A R L E T O N , POWER and BOYLE it became familiar to seventeenth century readers.



454 C. WEBSTER:

I t w a s o f t e n e x p r e s se d a s "elatery" a n d u s e d a s a n a d j e c t i v e . T h i s t e r m p r o b a b ly

s u g g e s te d t h e a n a lo g o us E n g l i s h t e r m " s p r in g " w h ic h BO Y L E p r e f er r e d . Bo th

" s p r in g " a n d "e l a t e r " g r a d u a l ly f e ll in to di su s e, b e in g s u cc e e d e d b y "e l a s t i-

c i t y " .

PECQUET adop ted a t r ans l i te r a t ion o f ~a~d~ (dast icus," propu ls ive o r

impu ls ive) , and th i s t e rm was ado p ted by POWER, BOYLE, HOOKE and HENRY

MORE, and has beco me the s tan dard Eng l i sh te rm e xpress ing the r ever s ib le

ex tens ion and con t r ac t ion "of phys ica l bod ies. PECQUET expressed h is con cep t

o f a i r a t the beg in n ing o f hi s accoun t . Th is shows c lear ly the fu s ion o f the ideas

whi ch ori gin ate d fro m BEE CKMAN an d ROBERVAL.

It is my suggestion to you that this (air) is like spongy or more woolly heapsly ing on the matter of the Terraquaceous Globe; as a consequence of which each

successively higher layer compresses the lower; they are sustained so that , the n earerthe layers are to the earth, then also tl~ey are more closely compressed by the weightand pressure of those ly ing on them. On acco unt of the spontaneous d i la ta tion , whichI cal l Elater , however s trongly they are compressed by the cumulat ive burden , i fset free the ' air rarities.

Hence, I in fer tha t such lower par ts tha t are subjected to the whole burden ,so that of a l l par ts they have the maximum degree of condensat ion . Because of th issame cause, whereby i t exer ted i ts powerfu l tendency to rarefy , not only by meansof its weight but also by its elater pressing against the surface of the Terraquac~ousglobe . 39

The a ims o f PECQUET'S expe r ime n ts were l imi ted ; he p ropos ed the hypo-

thes i s o f the e las t ic i ty o f a i r and p roduced a se r ies o f exper imen ts to ver i fy th i s .O n ly s l i g h t a t t e n t i o n w a s p a id t o t h e p l e n i s t - v a c u i s t c o n t r o v e r s y , a n d h i s o n ly

excu r s ion in to the po lemic was to po in t ou t tha t DESCARTES ' ae the r th eo r y cou ld

n o t e x p l a in t h e c a r p - b l a d d e r e x p e r im e n t . I t i s p r o b a b le t h a t P ECQU ET , l ik e

ROBERVAL, r e ta ined the idea o f the hom ogen e i ty o f a ir , in keep ing w i th the

Ar is to te l ian idea o f r a r e fac t ion , b u t h i s te rmino l ogy was su f f ic ien t ly sugges t ive

to r e lay to the E ng l i sh au tho r s , the idea o f sp r ing -l ike par t ic les suspended in a

m o r e r a r e f i e d m e d iu m .

V . T h e I n t r o d u c t i o n o f E x p e r i m e n t s o n A i r P r e s s u r e i n t o E n g l a n d

I t i s p r o b a b le t h a t t h e p e r f o r m a n c e o f t h e T o r ri c e ll i an e x p e r im e n t i n F r a n c e

p r e c e d e d i t s i n t r o d u c t io n i n to E n g la n d , b u t t h e d e l a y c o u ld n o t h a v e b e e n l o n g ,

•s ince JOHN WALLIS reco rded t ha t " th e weigh t o f A i r, the Poss ib i l i ty o r Im pos -

s ib i l i ty o f Vacu i t ies, and Nat u re ' s abhor rence thereo f , the Tor r ice l lian Exper i -

me n t in Qu icks i lver , " 4o were am ong the sub jec ts d i scussed a t the w eek ly sc ien t if ic

meet ings in London . The g roup per fo rming these exper imen ts inc luded JOHN

WILK INS, JONATHAN GODDARD, GEO RGE ENT, FRANCIS GLISSON, CHRISTOPHER

MERRET, SAMUEL FOSTER an d THEODORE HAAK, wh o wer e am on g the na tio n 's

mos t d i s t ingu ished na tu ra l ph i lo sopher s . In abou t 1648 th i s g roup ex tended

th e i r a c t i v i t i e s to O x f o r d, a n d t h i s i n t r o d u c e d t h e T o r r i c e l li a n e x p e r im e n t t o

a wide r group, which soon include d ROBERT BOYLE.

3, Ibid., p. 8.9.4o JOHN ~VALLIS, le tt er to Dr. SMITH, 29th Ja n. , 1696/97; this is foun d i n Peter

Langto]t's Chronicle, ed. T. HEARNE, Oxford, 1725, 2 v ols.; vol. !, Ap pen dix xi,pp . c lx i- -clx iv .



B o y l e ' s L a w a n d t h e E l a s t i c i t y o f A i r 4 55

THEODORE H A A K w a s p r o p o s e d b y W A LL IS a s t h e i n i t i a t o r o f t h e s e r e g u l a r

s c i en t i fi c m e e t i n g s , a n d i t w a s p r o b a b l y h e w h o i n t r o d u c e d t h e T o r r i c e l l i a n

e x p e r i m e n t : t o t h e ' S o c i e t y , s i n ce he h a d t r a v e l l e d e x t e n s i v e l y i n E u r o p e a n d w a so n e o f ME R SE N NE 'S c o r r e s p o n d e n t s . I n t647 h e r e s u m e d c o n t a c t w i t h M E R S E N N E

a f t e r a b r e a k o f n e a r l y s e v e n y e a r s , a n d i n a l e t t e r o f 2 4 M a r c h / 3 A p r i l , t 6 4 8 ,

h e t h a n k e d M ER SE NN E f o r t h e c o m m u n i c a t i o n o f t h e e x p e r i m e n t , a n d r e p o r t e d

t h a t ' i t h a d a l r e a d y b e e n p e r f o r m e d b y h i s f r ie n d s .

~We h a v e m a d e t w o o r t h r e e t r i a l s o f i t , i n t h e c o m p a n y o f I n e n o f l e t t e r s a n d

r a n k . . . I s h a l l a t t e m p t t o e n c o u r a g e s o m e o f t h e b e s t w i t s t o m a k e .s om e i n v e s t i g a t i o nof the basis of these observations. 1

In another letter of 3/13 July, he reported placing water with the mercury

in the experiment, and their unsuccessful trims of the vacuum-in-vacuum ex-

periment, of which he wished M ERSENNE to provide more details. 2SAMUEL HARTLIB (1595 /1600 - -1662 ) , 43 wh o wa s an o t he r o f MERSENNE'S COY-

r e s p o n d e n t s , f r i e n d o f H A A K a n d p u b l i c i s t o f s c i e n t i f ic i n f o r m a t i o n , a l s o k n e w o f

t h i s i n t e r e s t i n a i r p r e s s u r e , a n d i n M a r c h 1 6 46 /7 h e i n f o r m e d B OY LE o f h i s s u p p o r t

o f MERSENNE'S op in ions .

. . . and now i t comes i n to m y mind , I r ead , no t l ong s ince , i n a l a t e me chan ica lt r e a t i s e o f th e e x c e l l e n t M e r s e nn e s , b o t h t h e c o n s t r u c t i o n a n d u s e o f t h i s e n g i n e

( w i n d -g u n ) , a n d a m o n g s t • t h e u s es , o n e, w h o s e s t r a t a g e m o b l i g e d m e t o t a k e o f i tp a r t i c u l a r n o t ic e ; a n d i t w as , h o w b y t h e h e l p o f t h i s i n s t r u m e n t t o d i s c o v e r t h e

w e i g h t o f t h e a i r, w h i c h , f o r a l l t h e p r a t t l i n g o f o u r b o o k p h i l o s o p h e rs , w e m u s t

be l i eve t o be bo t h h ea vy and pond e rab l e , i f we wi ll no t r e fuse be l i e f t o ou r s enses . 4~

I n a l e t t e r o f M a y 1 64 8, w e f i n d H AR TL IB a g a i n p r o v i d i n g B OY LE w i t h i n f o r m a -

• t i o n a b o u t e x p e r i m e n t s o n a i r p r e s su r e ; t h i s t i m e a s a n e x t r a c t f r o m o n e o f S i r

CHARLES CAVENDISH'S le t te rs , w hi ch wi l l be soo n qu ot ed in fu l l . 45 BOYLE ha d

c o n s e q u e n t l y m a n y . y e a r s a c q u a i n t a n c e w i t h t h e p r o b l e m o f a i r - pr e s s u re , b e f o r e

h e h a d b e g u n t h e c o n s t r u c t i o n o f h i s f i rs t a ir p u m p , a n d i t is p r o b a b l e t h a t t h e

T o r ri c e ll i an e x p e r im e n t w a s f r e q u e n t l y d e m o n s t r a t e d a t t h e L o n d o n a n d O x f o r d

m e e t i n g s o f t h i s E n g l i s h v i r t u o s i . T h u s , w h e n w r i t i n g h is New Exper imen ts Phys ico -

~x L et te r fro m THEODORE HAAK to MERSENNE,24 th March /3 Apr i l , 1648 ; quo ted

from HARCOURT. BROWN, Scienti/ie Organisations in seventeenth century Pr an ce ,

1620--1680, Ba l t im ore , 1934, p . 58¢2 L et te r fro m THEODORE I-IAAK to MERSENNE, 3/13 July , 1648. T his i s g ive n

i n th e F r e n c h in P a s c a l ' s Oeuvres, op . c i r. , vo l . I I , p . 307 . A t r an s l a t i on o f t h i s pa s sage

i s g i v e n b e l o w . - - " W e h a v e a l s 0 t r i e d t o m i x w a t e r w i t h t h e m e r c u r y i n t h e t u b e ,a n d w e f i n d n o t a b l e v a r i a t i o n s i n i t , w h i c h w i l l c a u s e u s t o b e m o r e p r e c i se in o u r

o b s e r v a t i o n s i n f u tu r e . I w o u l d l i k e t o l e a r n h o w y o u a r r a n g e t h e e x p e r i m e n t s s o

a s n o t t o s p o i l a n d l o se c o n s i d e r a b l e a m o u n t s o f m e r c u r y ; a n d i f y o u m a k e u s e o f

• e x a c t g la s se s r a t h e r t h a n a n y t h a t c o m e to h a n d . A l s o, I d o n o t u n d e r s t a n d t h e m a n n e r

Of p e r f or m i n 'g y o u r l a s t e x p e r i m e n t o f t h e o n e t u b e i n t h e o t h e r , i n w h i c h [ t he v a u u m ]

s h o u l d e m p t y e v e r y t h i n g , s e e i n g a s w e h a v e n o t y e t s u c c e e d e d i n t h i s a t t e m p t . "

as The r e l a t i on sh ip o f HAAK and HARTLIB wi th t h e ea r ly Roy a l . Soc i e ty has b eencons ide red by Mis s JR. H . SYFRETT, The Or ig i ns o f t h e Roya l . Soc i e ty , Notes and

Records o/the Royal Society, 1948, 5, pp . 7 5 - -137 ; G . H . TURNBULL,S a m u e l H a r t l i b ' s• i n f lu e n c e o n t h e e a r l y h i s t o r y o f th e R o y a l S o c i e t y , Notes and Records o~ the Royal"Society, 1953, 10, pp. 101-= -t30; PAMELA 1~. ~[3ARNETT,T h e o d o r e H a a k a n d t h e e a r l yy e a r s o f t h e R 6 y a l S o c i e t y , ~qnnals o/ Science, t 957 , 13, pp . 20 5 - - 2 t8 .

4,4 SA.NIUELHARTLIB, le t t e r to ~OYLE, 19th March, 1646/7; ]3OYLE'S Works, o p . c i r . ,vol. ~, p. 22.

48 SAMUEL HARTLIE, le tt er to BOYLE, may , 1648 ; Works, :op. cir. , vo l. 5, p. 257.



456 C. WEBSTER:

Mechanica l l in 1659, he referred to his conj ectu res about the e xperime nt when

he had "severa l years before often made the experi ment de vacua with my own

han ds. " 46

Had HARTLIB not received informa t ion about the Torricel l ian experimen t

fro m HAAK, he could ha ve obt ain ed it fro m WILLIAM PETTY, who rec eiv ed infor-

at i0 na bo ut rec ent rese arch in F ra nc e from Sir CHARLES CAVENDISH. This le tt er

was pas se d on to HARTLIB and is pre ser ved in his papers.

April 7/t9, t648 , Paris. To Mr. Petty .

Worthy Sir,

My thankes was due to you long since for many favours received from you andparticularlie for your letter wherein you are pleased to acquaint me with some of

your new discoveries in Anatomie, and Inquires of other usefull and ingenious know-

ledges and your.invention of writing in many Copies at once, for all which I give

you ma ny thankes" and ha d done it sooner but tha t I hoped to have ha d some new

book or invention of our rare men here to informe you off, but knowing nor hearing

of any 1 thou ght fit though to trouble you to acknowledge your favours by this

Letter. I showed Mr. Hobbes yo ur L ette r who liked it soe well tha t he desired me

to send it him wh ic h I did knowing him to be your frie nd. He is not now here

otherwise I know hew ou ld either have write to you or desired me to rememberhim to you. Your worthy Friend and myne Mr. Gassend is reasonable well and hath

Printe d a Book of Ye Life and Manners of Epicurus since your going from hence

as I thinke. He hath now in ye Presse at Lyons, ye philosophie of Epicurus in which

I beleeve wee shall have much of his owne philosophy which doutlesse will be anexcellent worke. There is an Experiment, how to show as they suppose that there

is, or may be, vacuum. It may bee it was here before you went from hence. It weretoo long to recite all the particfllars, but ill brief thus, t he y prepar e a long tube like

a weather-glasse, which is filled with quicksilver, and being stopt as close as maybe with ones finger the tube is inverted and plunged in a vessell halfe or more full

of quicksilver. The quicksilver in ye tube will force Ye quicksilver in ye vessell to

rise by adding more quick silver to it, and so leaves a space in ye top O the tu be

vacuum as is supposed but a bladder being hung in that vacuum, was as perfectly

seene as could be, so that there must bee some body there to convey ye Action oflight to ye and you as I suppose and divers others heere, that the bladder was made

as flat as they could, then the y put it in, a nd when then quicksilver lefff it, it swelled

in that supposed vacuum like a little football. Sir I have troubled you much there-fore com mit tin g you and us all to Go d's holy protection. I remame.

Your assured friendSo serve you

Charles Cavendish 47

Sir CHARLES CA~CENDISH'(1591 t654 ), *s th e au th or of thi s le tt er , was an

exi le in Europe during the Civi l War and he spent three year s in Paris , beginning

46 ROBERT BOYLE, New Experiments Physico-MechanicaU, Oxford, 1660; ~Vorks,op, cir . , VO1. ], p. 5- BOYLE may have been r eferring to the commun icati ons b etwe en

England and France in 1647 and t648 when he noted: "perceivi ng by lettersfrom other ingenious persons at Paris, that several of the Virtuosi there were very

intent upon the examination of the interest of the air, in hindering the descent of

the quicksilver, in the famous experiment touching the vacuum; I thought I couldnot comply with your desires in a more fit and seasonable manner, than by prosecutingand endeavouring to promote tha t .noble exper iment of Torricellius." Ibid., p. 5.

47 This letter is in the Hartlib papers, Sheffield University Libral-y, Brindle VII,

no. 29.4s JEAI~ JACQUOT, Sir Charles Cavendi sh and his lear ned friends, Annals ol Science,

t952, 8, pp. 13 27, 175 194.



Boyle 's Law and the Elast icity "of Air . 457

in t645. He became acq uai nted with MERSEN~'E and DESCARTES and was con-

versant with a wide range of scientific developments. The Cavendish family

were p atrons of THOMAS HOBBES, who was ment ion ed in the above letter, andwho later became a participant ill the discussions of air pressure.

Thus, even withou t direc t access to the writings of PASCAL and TORRICELLI

on air pressure, English natural philosophers had ample evidence of the continental

research on air pressure, from informal exchanges of correspondence aiTd the

publ icat ions of MERSENNE, GASSENDI, PECQUET, PETIT, iNOJ~L and PASCAL, as

well as certain Italian works.

The first published description of the Torricellian experiment by an English

author , which I ha ve been able to trace, was by WALTER CHARLETON (1619- -

1707) . H e was educate d at Oxfo rd University, where he received his M.D. in

t641, and his first published works were concerned with medicine, but in 1654he turned his attention to wider philosophical problems. His works Were mainly

derivative, although they betrary wide reading.

His influential work, P h y s i o l o g i a E p i c u r o - G a s s e n d o - C h a r l t o n i a n a , 4~ of 1654,

contained a detailed discussion of the controversies between the plenists and

vacuists, which had !argely overshadowed the experimental studies of the physical

properties of air by French authors. Interest in the 'Torricellian experiment was

closely related to this metaphysical discussion, since its interpretation determined

the alignment with either the Cartesians or Gassendists.

With CHARLETON, as with the Frenc h authors, interest in the Torricellian

experiment as a problem in experimental physics, was allied to its relevance to

the problem of vacuum. The long fourth chapter of Book I Of P h y s i o l o g i a was,

concerned with the establishment of the v a c u u m d i s s e m i n a t u m and v a c u u m

coacerva tum, and it was as Support for the latter notion that he introduced the

Torricellian experiment.

CHARLETON referred to the experiment as a:

Welcome opportunity to challenge all the Wits of Europe to an aemulous combatfor the honour of perspicacity. Now albeit we are not yet fully convinced, that thechief Phaenomenon in this illustrious Experiment doth clearly demonstrate t h eexistence of a Coacervate Vacuity, such as thereupon by many conceded, and withall possible subtlety defended by that miracle of natural Science, the incomparableM e r s e n n us (in reflexionibus Physicomathemat) yet, insomuch as it affords occasionof many rare and sublime speculations, whereof some cannot be solved either sofully, orperspicuously by any Hypothesis, as that of a V a c u u m D i s s e m i n a t u m a m o n g

the insensible particles of Aer and Water; and most promise the pleasure of Novelty,if not the profit of satisfaction to the worthy consider; we judge it no unpardonable

49 .WALTERCHARLETON Physiologica Epicuro-Gassendo-Charl toniana: or, a 'Fabrich

o /Sc ience Na tura l , Upo n the Hypo thes i s o / A toms, London, ! 654. Although CHARLETONquoted a wide range of authorities, he had probably not read more than a few ofthem and most of his information was abstracted from GASSENDI'Swork. In France,there had been discussion about the origins of the Tolxicellian experiment and KIRCHER

acknowledged TORRICELLI'Spriority, although he must have been acquainted withBERTI'S work. CHARLETONquoted from ]KIRCHER'S account and in England therewas general and unquestioning acceptance of TORRICELLI'Spriority. -- "... never-theless, it is ascertained to my satisfaction that the experiment was first inventedby Torricelli, mathematician to the noble and great Duke of Florence " W CHARLETON,

op. cit., p. 35; A. KIRCHER, Afusurgia universal i s s i re Ars magna consoni e t d isoni ,

Rome, 1650, p. 11.

Arch. Hist. Exact Sci., Vol. 2 3i



458 C. WEBSTER:

D i g r es s io n , h e r e t o p r e s e n t t o o u r j u d i c i o u s R e a d e r , a f a i t h f u l T r a n s c r i p t o f t h e

E x p e r i m e n t , t o g e t h e r w i t h t h e m o s t r a t i o n a l s o l u t i o n s o f a l l a d m i r a b l e A p p e a r e n c e sobse rved the re in . . . s0

T h e a c c o u n t o f t h e e x p e r i m e n t w a s t o t a l l y d e r i v a t i v e , a n d t h e m e r c u r y h e i g h t

i n t h e T o r r i c e l l i a n t u b e w a s g i v e n a s 2 7 i n c h e s . 51 H e o v e r l o o k e d t h e f a c t t h a t

t h e F r e n c h i n c h w a s a l a r g e r u n i t t h a n t h e E n g l i s h , a n d i n E n g l i s h i n c he s t h e

h e i g h t w o u l d h a v e b e e n 2 9 i n c h e s. H e ~ n 0 t e d t h a t w a t e r s h o u l d r i s e t o 3 2 f e e t

i n t h i s e x p e r i m e n t , b u t s h o w e d n o p r a c t i c a l k n o w l e d g e o f i t s t r i a l . 52

Host of CHARLETON'Sa c c o u n t w a s d e v o t e d t o a r e p e t i t i o n o f GASSENDI'S

j u s t i f ic a t i o n o f t h e E p i c u r e a n . a r g u m e n t s i n f a v o u r o f V a c u u m i n N a t u r e , a n d

t h i s l e d h i m t o d i s c u s s t h e r a r e f i c a t i o n a n d c o n d e n s a t i o n o f a i r . I t h a s b e e n

n o t e d t h e E p i c u r e a n e x p l a n a t i o n o f c h a n g e i n d e n s i t y b y" t h e a l t e r a t i o n o f t h e

r a t i o o f v o i d t o m a t t e r i n a b o d y , a n d t h e c o n d e n s a t i o n a n d r a r e f a c t i o n o f v o l u m e so f a i r p r o v i d e d e x t r e m e e x a m p l e s o f c h a n g e i n d e n s it y . H e e x p l a i n e d t h is b y

r e f e r e n c e t o t h e p r i n c i p l e o f t h e d i s s e m i n a t e v a c u u m . T h e a i r in a c l o s e d s p a c e

w a s a n a l o g o u s t o a v e s s e l f i ll e d w i t h w h e a t s e ed s o r s a n d p a r t i c l e s ; b y t h e a p p l i c a -

t i o n o f a g r e a t w e i g h t t h e p a r t i c l e s c o u l d b e c o m p r e s s e d t o o c c u p y a s m a l l e r v o l u m e .

T h i s w a s e x p l a i n e d b y t h e c l o s u r e o f t h e s p a c e s b e t w e e n t h e p a r t i c l e s.

So l i kewi se a r e t he pa r t i c l e s Of a i r i nc luded in t he fou r - inch space o f t he Tube ,b y C o m p r e s s i o n o r C o a n g u s t a t i o n r e d u c e d d o w n e t o t h e i m p l e t i o n o f o n e l y t h e h al ~

o f t h a t s p a c e ; b e c a u s e fr o m a m o r e l a x o r r a r e C o n t e x t u r e t h e y a r e c o n t r a c t e d i n t oa dense o r c lo se , t he i r ang le s and s ides be ing by th a t f o r ce mo re d i sposed fo r r ec ip roca l

Con t ingence , and l eav ing le s s In t e rvM s , o r em pty spaces be t ;w ix t t he m then be fo re . 53

O t h e r e x p e r i m e n t s i n d u c e d h i m t o r e v is e " th is s i m p l e g e o m e t r i c a l e x p l a n a t i o n

a n d a d o p t a m o r e k i n e t i c m o d e l f o r t h e a i r. H e r e c o g n is e d t h a t t h e i n t r o d u c t i o n

o f a s m a l l v o l u m e o f a i r i n t o t h e s p a c e a b o v e t h e m e r c u r y i n t h e T o r r i c e ll i a n

e x p e r i m e n t c a u s e d a n i m m e d i a t e a n d v i o l e n t d e s c e n t o f t h e l iq u i d , a n e f fe c t

o u t o f a l l p r o p o r t i o n t o t h e v o l u m e o f a i r i n t r o d u c e d . 5~ H e a l s o n o t e d t h a t t h e

W i n d - G u n i l l u s t r a t e d t h e e x p a n s i o n a n d c o m p r e s s i o n o f a i r, a d o p t i n g t h e t h e o r e -

t i c a l m o d e l o f a i r as m a s s o f s p r i n g - l i k e p a r t i c l e s .

F o r , a s t h e i n s e n si b l e p a r t i c l e s o f t h e A e r i n c l u d e d i n t h e T u b e o f a \ ¥ i n d - G u r i ,

b e i n g, b y t h e E m b o l o u s o r t Z a m m e r , fr o m a m o r e l a x a n d r a r e c o n t e x t u r e , i l l o r d e r,

r e d u c e d t o a m o r e d e n s e a n d c l os e (w h i c h i s e f f e c te d w h e n t h e y a r e m a d e m o r e c o n -t i guous i l l t he po in t s o f t he i r supe r f ice , a l ld SO com pe l l ed t o d imin i sh t he i nane spaces

i n t e r j a c e n t b e t w i x t t h e m , b y s u b i n g re s s i 0 n ) ar e , in a m a n n e r s o m a n y S p r i n g s o rE l a t e r s , s u c h w h e r e o f , s o s o o n a s t h e e x t e r n a l F o r c e , t h a t c o m p r e s s e d t h e m , c e a s e t h

( w h ic h is a t t h e r e m o v e o f t h e D i a p h r a g m e o r p a r t i t i o n p l a t e i n t h e c h a m b e r o f t h e

T u b e ) r e f l e c te t h , o r i s a t l e a s t r e f l e c t e d b y t h e i m p u l s e o f a n o t h e r c o n t i g u o u s p a r t i c l e. 55

T h i s c o n c e p t u a l m o d e l o f a ir a s a m a s s o f s p r i n g - l i k e p a r t i c l e s is u s u a l l y

a t t r i b u t e d t o B OY LE , b u t i t h a d p r e v i o u s l y b e e n i m p l i e d in P EC gU E T'S b o o k , a s

w el l a s i n CHARLETON'S. 56

5o Ib id . , pp . 3 5- -3 6 .

~ Ib id . , p . 36, t h i s ac coun t was t ak en f rom GASSENDL and i t i s f ound in OperaOm'nia, Ly on s, 1658, vo l . t , p. 204.52 W. CHARL!ETON,1654, op . cit. , p. 52.

~ I b id . , p . 26 .

54 Ib id . , pp . 55- - 56 .5~ Ib id . , pp . 55- - 57 .5s See Append ix 5 .




VI.'Henry Power's Experiments of 1653

W r i t i n g a t t h e s a m e t i m e a s CH AR LE TO N W a s H E N R Y PO W E R ( t 6 2 3 - - t 6 6 8 ) ,

w h o a d o p t e d a m o r e e x p e r i m e n t a l a p p r o a c h t o t h e p r o b l e m o f a i r p r e ss u r e .P O W ER w a s b o r n a t H a l i f a x i n Y o r k s h i r e a n d w a s e d u c a t e d a t C h r i s t ' s C o l le g e ,

C a m b r i d g e , w h e r e h s o b t a i n e d h i s M . D . in t 6 5 5 . D u r i n g t h e e a r l y p a r t o f h i s

f o u r t e e n y e a r s a t C a m b r i d g e , h e b e c a m e a n e n t h u s ia s } i c e x p e r i m e n t a l s c ie n t i s t ;

a n d h i s f i r s t w r i t i n g s w e r e o n c i r c u l a t i o n a n d t h e l y m p h a t i c s y s t e m . 57 T h u s , i t

m a y h a v e b e e n PECQUET'Sb o o k w h i c h t u r n e d h i s a t t e n t i o n t o w a r d s t h e s t u d y

o f a i r p r e s s u r e a n d i t i s p r o b a b l e t h a t t h e T o r r i c e l l i a n e x p e r i m e n t w a s c O m -

m o n l y p e r f o r m e d a t C a m b r i d g e , b y t 6 5 3 . L i k e C HA RLE TO N, P O W E R .W a s s t r o n g l y

i n v o l v e d i n t h e G a s s e n d i s t - C a r { e s i a n d i s p u t e s , a n d , u n d e r t h e i n f l u e n c e o f H E N R Y

M O RE , C h r i s t ' s C o l le g e w a s t h e c e n t r e f o r C a r t e s i a n t h o u g h t i n E n g l a n d . ,

P O W ER p e r f o r m e d h i s f ir s t se r ie s o f e x p e r i m e n t s o n a i r p r e s s u r e a t C a m b r i d g e

a n d H a l i f a x i n t 6 5 3 , b u t h i s a c c o u n t w a s n o t f i n a l l y e d i t e d f o r p u b l i c a t i o n u n t i l

t 6 6 3 , t h e e x p e r i m e n t s f o r m i n g t h e f i r s t p a r t o f B o o k I I o f h i s o n l y w o r k ,

Experimental Philosophy, w h i c h a p p e a r e d i n t h e a u t u m n o f 1663~5s T h i s d e l a y

i n p u b l i c a t i o n h as c a u s e d n e g l e c t o f t h e s e p i o n e e r E n g l i s h e x p e r i m e n t s o n a i r

p r e s s u r e .

E v e n t h o u g h P O W ER w a s a n o b s c u r e p e r s o n a t t h i s t i m e , h is w o r k w a s c i r c u -

l a t e d a m o n g n a t u r a l p h i l o s o p h e rs a s l a t e a s t677. 59 T h e e x p e r i m e n t s w e re

n d t . w i t h o u t i n t e r e s t s i n c e i n f o r m a t i o n a b o u t t h e m r e a c h e d H A RT LIB . R ~L P H

G REA TO RE X, w h o p r o v i d e d h i m w i t h t h e i n f o r m a t i o n , w a s o n e o f t h e m o s t

c e l e b r a t e d L o n d o n i n s t r u m e n t m a k e r s . H e w a s s o o n i n v o l v e d il l t h e d e s i g n of

a n a i r p u m p f o r RO B E RT B O Y LE . H A R T LtB r e p o r t e d :

O n e I B il !i ng s le y a s c h o o l m a s t e r l i v e s i n a g e n t l e m a n ' s h o u s e , w r i t e s o n D r . P a s c a l ' s

r a r e e x p e r i m e n t s o f q u i c k s il v e r - - t r i e d a n d a u g m e l i t e d b y H e n r y B o w e r E sic.] 1 65 3,

2 M a y E sic .] w h i c h h e i s t o p u b l i s h i n t h e g e n t l e m a n ' s n a m e .

57 H E N R Y P O W ER , " C i r c ~ l a t i o s a n g u i n i s i n v e n t i o H a r v e i a n a , ? ' I BM Sloane M S t 3 4 3 ,

f t. 3 - - 4 0 ; " i n v e n t i o A s e l l i a n a d e V e n is L a c t e i s e t d e M o t u C h y ! i , " I b i d . , f t. 4 1 - - 5 6 .5s T h e r e a r e t h r e e r e m a i n i n g v e r s i o n s o f P OW E R'S t 6 5 3 e x p e r i m e n t s . T h e y w i l l

b e r e f e r r e d t o a s t e x t s A, B, a n d C . - - A , " E x p e r i m e n t a M e r c ur ia l ia n u p e r m i h i

e x h i b i t a a v i r o u n d i q n a q u e o r n a t is s i m o D . D o m i n o H e n r i c o P o w e r M e d ae- D o c t o r a e

H a l l i f a x a e . A n n o D o m i n i 1 7 0 3 , " I B M Sloane M S t 32 6 , f f . t 3 3 - - 1 4 1 . 'T h e d a t e o ft h i s w o r k i s a d d e d t o t h e o r i g i n a l m a n u s c r i p t a n d i s i n c o r r ec t ; i t s h o u l d r e a d t 6 53 . - -B, "Dr. P a s c a l l ' s r a r e e x p e r im e f i t s o f 9 t r y e d a n d a u g m e n t e d b y H e n r y P o w er ~

t 6 5 3 , M a y 3 r d , " B B od le ia n L i b r a r y , Ashmolean M S t 4 0 0 , ft . 1 5 ~ 2 1 . - - C , " P h y s i c o -M e c h a n i ca l E x p e r i m e n t s t r y e d i n t h e y e a r e 1 65 3 b y H e n r y P o w e r , " I BM , SloaneR ¢S 13 9 3, f t . 1 3 4 - - 1 5 3 . m O n l y v e r s i o n C is i n P O W ER 'S h a n d w r i t i n g , a n d i t is * h em o s t c o m p l e t e a c c o u n t o f t h e e x p e r i m e n t s . I t w a s t h i s v e rs i o n w h i c h w a s i n c o r p o r a t , d

i n h i s p u b l i c a t i o n o f 1 66 3. I w i l l r e f, er t o C , u n l e s s o t h e r w i s e s t a t e d , - a n d t h e p a g er e f er e n c e s w i ll b e t o t h e p u b l i s h e d a c c o u n t : Experimental Philosophy, in Three Books:Conlaining Ne~e~ Experiments Microscopical, Mercurial, Magnetical. With some De-ductions, and Probable Hypotheses, raised [rom them, in Avouchment and illustrationo/ the.now /amous Atomieai Hypothesis, L o n d o n , t 6 6 4 , [ t6 6 3 ~ . V e r s i o n C o c c u p i e s

p p . 8 8 - - 1 2 1 . - - W h i l e V e r s i o n C g i v e s a g o o d i n d i c a t i o n o f P OW E R'S e x p e r i m e n t so f 1 65 3, i n t e r n a l e v i d e n c e s u g g e s t s t h a t i t is a r e v i s e d a c c o u n t o f a n e a r l i e r m a n u s c r i p t .T h u s v e r s i o n s A a n d B m a y g i v e a b e t t e r i n d i c a t i o n o f t h e f i r s t d r a f t o f t h i s w o r k .

59 T h e r e i s a n o t e a p p e n d e d t o B ; ' "V V r it te n b y J o h n S p o n g e , c a m e a f t e r t o R o b ' tT u r n e r , t h e n t o M r . D U CG ET T, f r o m h i m t o m e E S t a n s b y ] y e 1 S e p t . 1 6 7 7 " . f . 1 3 a .

JO HN S P o N ~ ( 1 6 2 3 - - p o s t 1668) w a s a m a t h e m a t i c a l p r a c t i t i o n e r a n d i n s t r u m e n tm a k e o f L o n d o n

3 t *



460 C. WEBST~ER

He hath re-experimented them all and pu t new experiments to it. s°

POWER left Cambridge, in 1654 or t655, without hav ing published these

experiments, and he spent his remaining years in the West Riding of Yorkshire,paying only occasional visits to London and Cambridge. He was thus separated

from the main centres of scientific activity and had 'little oppo rtun ity to augmen t

and publish his work. As will be explained later, these circumstances altered

when the Royal Sociei:y was instituted. In t660 he re suscitated his earlier scientific

writings and returned to the experimental study of air pressure.

P0WER'S work is a great con tra st to CHARLETON'S.He showed knowledge of

PECQUET'Sbook only, as the source of his knowledge of'the French investigations,

and like PECQUEThe presented a series of briefly described experiments, indicat-

ing their relationship to his hydrostatical and pneumatical hypothesis. However,

his metaphysical position differed from PECQUET,who had adopted ROBERVAL'Sthe ory of rarefaction ; while POWER held Cartesian plenism.

It is probable that POWER had already ad opted the Cartesian th eory of

matter before he was introduced to tile French experiments on air pressure.

He believed that air consisted of infinitely divisible "corpuscles" or "atoms"

suspended in an "aether" or "subtle matter". He now was introduced to the

hypothetical model of air proposed by PECQUET, and this influenced him to

introduce the concept of the innate activity of the particles of matter, differing

from DESCARTES who believed th at the moti on of the corpuscles was due to the

ac tiv ity of the aether. POWER now accorded the aether a more passive r-61e, as

the innate substratum for the particles. This view differed from that of PE~QUETin adopting a more literal.interpretation of the spring-like nature of the particles

of air, and in introducing the Cartesian aether as the substratum for them. A

full quota tion of POWER'S theo ry is given as A ppendi x IV. 61 This assimilation

of the Aristotelian concept of active rarefaction into the structural characteristics

of the corpuscular theory was a valuable imaginative aid in the later quantita tive

studies of the elasticity of air.

The s tarti ng point of POWER'S experiments had been t he Torricellian experi-

men t, 62 and like CHARLETO~¢, he was hesi tant in giv ing his own experimenta l

results which differed from those .of the Fren ch authors. Only the last versiongave the height of merCjary as 29 inches although he was aware of the difference

between English and French measure 6~ in the earliest composed "~ersion A".

:so SAMUEl. HARTLIB, Ephemerides, 1655. This is a journal kept by HARTLIB\

between t634 and t660; it is in the Sheffield University Library. In t654, HARTLIBhad referred to BILLINGSLEYas he "who necessitated to follow heterogeneous im-ployments as I take it Physick, but his whole genius is bent towards the mathematicksand mechanicks in which he excels." ROBERTBILLINGSLEY was a school-master atthe Free School, Thurlow, Suffolk.

61 Version C pp. t01- -t03 .6~ It was no t until version C that POWBR mentioned TORRICELLIUS(p. 90) or

PARICELLIUS (p. 93)!s3 In version C he noted that the. difference between .the French and Englishresults "may partly arise from the variations of the climates, the Air being morethin and hot then ours, partly from the difference and altitude of the. atmospherehere and there .,., and partly from the diversity of our measures and theirs,"pp. 93 94. BOYLE ad reached similar conclusions in his 1659 experiments; Works

op. cit., vol. 1, p. 25.



L

Boyle's Law and the Elasticity of Air ' 461

It is also probable that air was not completely removed from the apparatus in

the early trials of the experiment. He varied tile diameter, length and shapes of

the tubes and in all cases the mer cu ry remained at 29 inches in vertical height•In a separate experiment, he studied the difficulty of removing air from tile

apparatus.

The interpretation of the space above the me rcury was of the greatest import-

ance to him. Since the mercury space could be completely replaced by water,

the space could not conta in air. 64 He was also satisfied that it contained neither

light nor mercury vap our alone. Although this "seeming vacui ty" h ad no positive

properties, it would transmit light and magnetism and it had extension, tile

Cartesian dete rminant of. matter• These three points, and the associated belief

that all action was by contact, convinced him that tile space could not be empty

and must contain an "aethe r". 65Like PASCAL, he noted that meteorological conditions influenced the mer cur y

leVel, and the possibility of us{ng the tube for weather-forecasting interested him

at various times from thi s date 66. PECQUET had given an account of PASCAL'S

Pu y de D6me experiment, and POWER was in a good position to repeat this,

since the hills rise steeply to t000 feet around Halifax. This is to be contrasted

with the position of BOYLE and HooKE, who were never able to give a satis-

fac tory verification of this expe riment, for want of high hills i n tile sout h-east

of England. On May 6th t653, he carried the Torricellian experiment to the sum-

mit of Halifax hill, to the east of Halifax. 67 The earliest account of this experi-

ment, although the brie2est, indicates the manner in which he reached the hypo-thesis tha t the height of all mountains could be derived b y proportion, from

the results of a barometric experiment•

84 HENRY POWER, version C, p. 100.8s Ibid., pp. 94--103.8~ HENRY POWER; in version B , f. 16, he noted "that 'if any thing considerably

hot or cold be apply'd to the top of the tube it will proportionally ascend or descend(as tile water in a weather glass though not by farr so much), the l!ke is to be observedin the changes of weather, and therefore it is not unalterable at all times of theyeare'! . - - In 1661 POWER and TOWNELEYreaffirmed the value of barometric readingsin reflecting the meteorological conditions. The mercury level did "vary and alter

its Standard, which we found it to do considerably; for sometimes it was half aninch higher or lower then the Mark and Standard we left it first at. I think, accordingto the variation of the Atmosphaere in its temperaturei and if you observe, strictly,you shall see that the Quicksilver in the Tube does never precisely observe the same

- StandArd not a day together, nay sometimes not an hour.' , H. POWER, 1963, op. cir.,p. ~ 23. - - BOYLE also ~aoted that the Torricellian tube "did sometimes faintly imitatethe liquor o f a weather glass." He attempted, to associate this fluctuation withmeteorological Changes and tide levels; 1660, op. c~t., Wor k s , vol. t, pp. 26--28.In his later works he frequently returned to this problem. On 1st January, 1662"M~. Croune was desired to write to Dr. Power to observe the weather at Hallifax,"T. BIRCH, History of the Royal Society, 4 vols., London, t756/7; vol. t, p. 68. Al-though there are no records of POWER'Ssttldies, the sys tematic meteorological records

of his colleague, RICHARD TOWNELEY, are preserved. His barometric records were•sent to ~BOYLE, and his rainfa ll measurements, were transmit ted, to th e R0yal Societyand CHARLES LEIGH; Boyle' s Works, ~'01. 5, p. t35; CHARLES LEIGH, Th'e NaturalHistorj~ of Lancashire, Cheshire an d the Peak,. in Derbyshire, Oxford, 1700, pp. 21--;25.

87 Halifa:~-Hill is 775 It. high• "BoYI£E and HoolcE overcame the deficiency o fhills by,car ry ing .th e Torricellian experiment to the top of i~ondon churches. BOyI-EI1662, op. cit., Works, voL 1, p. t02, vol. 5, p. 535.



462 C. WEBSTER :

H EN R Y PO WE R a t t e m p t e d t h i s e x p e r i m e n t o n 6 t h M a y 4 65 3, w i t h t u b e s o f v a r i o u sl e n g t h s a n d d i a m e t e r , o n H a l i f a x H i l l , w h i c h i s s i t u a t e d a b o v e t h e t o w n o f H ~ I i f a x .

T h e m e r c u r y c y l i n d e r w a s c a r r ie d t o t h e b a s e o f t h e h i ll an d t h e m e r c u r y r o s e

t o e q u a l 2 7 in c h e s, w h e n c e a t t h e s u m m i t o f t h e h i l l i t w a s s h o r t e r i n h e i g h t b3~4 /S ths . i nch , t h i s be ing nea r ly a who le i nch lower .

Th i s ex pe r i me n t wa s pe r fo rm ed w i th t ubes o f 45 a nd 35 ~- i nches i n l eng th , so

t h a t b y a n a l o g y a n d p r o p o r t i o n i n e a c h o f t h e se e x p e r i m e n t s , t h e p e r p e n d i c u l a rhe igh t o f Ha l i f ax h i l l exceeds 290 .2 /3 rds . ya rd s , t h a t i s 872 f ee t ; ( I e s t im a te t h a t

6 F re nch f ee t a r e equa l t o one Eng l i sh po l e ) . L ikewise t h i s " go lde n ru l e " app l i e si n t h i s a n d s u b s e q u e n t e x p e r i m e n t s :

{ i nches [ f al l i n me rcu r y ] : 3o0o [ f eet i n a l t i t u de ]

1 ,000 [ fee t in a l t i tud e] .t he re fo re ] { i nches [ f al l i n me rcu ry ] : - - ~ - -

W hic h , when r ed uced in to F re nch f ee t , cons t i t u t e s 800 f eet . L ikewise 100 F re nch

fe e t ( acco rd ing to Her igone ) equa l 109 Eng l i s h f ee t , so t h a t 800 F ren ch f ee t a r e

equ a l t o 872 Eng l i sh f ee t o r 290 .2 /3 rds . ya rd s , wh ich d i s cove r s t he he ig h t o f t h i sh i l l ve ry s a t i s f ac to r i l y .~

I n t h e f i n a l v e r s i o n o f t h i s a c c o u n t h e w a s s a t i s f i e d w i t h a g e n e r a l i s a t i o n

t h a t t h e h e i g h t o f h i ll s c o u l d b e f o u n d b y t h e p r i n c ip l e , b u t h e g a v e n o n u m e r i c a l

e x a m p l e ;

. . . . w e . m ig h t n o t o n l y M e c h a n i c a l l y f i nd o u t t h e P e r p e n d i c u l a r h e i g h t o f o u r

g r e a t H i l l h e r e a t Hal l i /ax , o r a n y o t h e r M o u n t a i n w h a t s o e v e r , b u t v e n t u r e n o t a b l ya t t he he ig h t o f t he A tmo sph e re i t s e lf . 69

P OW E R'S c o n f u si o n o v e r m a t h e m a t i c a l e x a m p l e s m a y h a v e b e e n t h e r e a s o n

f o r n o t p r e s e n t i n g h i s o r i g i n a l c a l c u l a t i o n s , b u t a l s o t h e e x p e r i m e n t a l i n a c c u r a c i e s

O n s u c h a s m a l l h i l l w o u l d p r e v e n t c o n s i s t e n c y o f r e su l t s . T°T h e c o n s i d e r a t i o n o f t h e e l a s t i c i t y o f a i r c o n t a i n e d P o w E R ' S m o s t o r i g in a l

e x p e r i m e n t s , a n d c o n c l u d e d t h e i n v e s t i g a t i o n s o f ~ 6 5 3 . H e f o l l o w e d P E C Q U E T

i n s t r es s i n g t h a t t h e e l a s t i c i ty o f a i r r e q u ir e d s e p a r a t e c o n s i d e r a t i o n f r o m i t s

d e n s i t y .

. .. t h e w h o l e m a s s o f A y r h a t h a S p o n t a n e o u s E l e t e r [ si c. ] o r n a t u r a l a p t i t u d ei n i t s el f t o d i l a t e a n d e x p a n d i t s e lf u p o n t h e r e m o v a l o f al l c i r c u m a m b i e n t o b s t a c l e s

V e r s i o n B , f . 1 39 . T h e c a l c u l a t i o n i n t h e m i d d l e o f t h e q u o t a t i o n h a s l i t t l e

c o n n e c t i o n w i t h t h e t e x t . - - I n v e r s i o n C ~,the m e r c u r y h e i g h t a t t h e b a s e o f t h e h i l lwas g iven a s 29 i nches, and the f a l l du r ing , t he a sc en t was " m ore t hen ha l f an i nch . "

p. 104.~9 Ve rsio n C, p. t 0 4 .T0 PO WE R s u g g e s t e d t h a t h i s h y p o t h e s i s f o r d e t e r m i n i n g t h e h e i g h t s o f m o u n t a i n s

shou ld be t e s t ed on Mou n t Tene r i f f ( 3 ,7 t I m . ) , i n t he Can a ry I s l ands . I t was gen e ra l l yc o n s i d e re d t h a t t h i s w a s t h e h i g h e s t m o u n t a i n i n t h e w o r l d ( v e rs i o n C p p . t 0 5 - - 1 0 6 ) ,

a n d s i x t e e n t h c e n t u r y a u t h o r s h a d e s t i m a t e d i t s h e i g h t a s 9 0 , 0 0 0 m. (ScALIGER)a n d ~

105,000 m. (PATRIZZO)- BOYLE and the me mb er s o f t he Ro ya l Soc i e ty a l so sug ges t edt h a t t h e T o r r i c e ll i a n t u b e s h o u l d b e c a r r i e d u p t h i s m o u n t a i n ; T . B IR CH , 1756/57op. cir . , vol . ! , p. 8; R. BOYLe, Cont inuat ion o/New Exper i rnenB Phys ico-Mechanical ,

Oxford , t 669? , Works , op . c i r ., vo l . 3 , pp . 2 25 - - 22 8 . - I n Oc tob e r , 1661 , GEORGESINCLAIR (d. t 696 ) e s t i ma ted t he he igh t s o f Sco t t i sh h i l l s by t he ba r om e t r i c me th od ,a n d h e , l i k e P o w e r , h a d b e e n s t i m u l a t e d b y PECQUET'S work . Whi l e POWER used

PASCAL'S Pl~lyde ]35me a l t i t ude a s h i s s t an da rd , S INCLAIR ob t a ine d h i s own s t an da r db y c a r r y i n g t h e t u b e u p b u i l d i n g s o f k n o w n h e i g h t . H e r e a c h e d a s i m i l a r c o n c lu s i o nto POWER, th a t t he ba r om e te r f e l l one i nch fo r eve ry 250 pace s a sce nded (4 ; 250 f t .) .Howeve r. , i t m us t be no t ed t ha t . PowER'S he ig h t fo r t he P uy de D6 me (3,000 f t .or 973 m~) was too. low; i t is actually 4,465 m. G~ORG~ SINCLAIR, A r s n o w e t m a g n agravitates et levitatis, Ro t t e r dam , t 669 , pp . i 25 - - t4 9 . F . CAJORI, H i s to ry o f de t e rmin a -t i o n s o f t h e h e i g h t s o f m o u n t a i n s , Isis , t929, 1 2 , p p . 4 8 2 - - 5 t 4 .





464 C. WEBSTER"

I n a f u r th e r e x p e r im e n t a tw e lv e - in c h t u b e w a s h a l f fi ll ed w i th w a te r , a n d

th i s w a s i n v e r t e d a n d t o t a l l y im m e r s e d i n a c y l i nd e r o f w a te r . I n t h i s c as e t h e

v o lu m e o f a ir w a s r e d u c e d. T h i s m o d i f i c a t i o n o f t h e e x p e r im e n t w a s ' p r o b a b lysugges ted by RICHARD TOWNELEY who h ad o r ig ina ted the exp er im en t in w h ich

the Tor r ice l l ian tu be was ¢om ple te ly im me rsed in Mercu ry ,~7

I t i s apparen t , f rom scru t iny o f the Tab le , tha t POWER'S r esu l t s were too

in c o m p le t e t o e n a b l e a n y s a t i s f a c to r y la w to b e i n d u c ed , b u t h e c o n c lud e d :

The descent or fa ll of the Quicksilver or Water , wa s-m ost notable ab ou t themi dst of the Tube, viz. v~hei1 it was eq ually f ill 'd with A yr an d Quicksilver, o r Ayra n d W a t e r 7 s

Th is genera l i sa t ion was co r rec t w i th in the con f ines o f these par t icu la r r esu l t s ,

b u tw o u ld n o t h a v e a p p l i e d fo r t u b e s o f d i f fe r e n t l e n g th s . I t a ls o s h ow s th a t ,

a t th i s t ime , POWER ~¢as concerned wi th com par in g the change in v o lum e o fthe a i r , a s an exp ress ion ~of i t s e las t ic i ty , w i th the he igh t o f th e me rcu ry co lum n

in t h e s a m e tu b e . H e w a s n o t t h e n c o m p a r in g t h e a i r ' s e l a s t i c i t y w i th t h e e x t e r n a l

p r e s s u re e x e r t e d o n i t , w h ic h m u ~ t be c a l c u l a t e d f r o m th e b a r o m e t r i c h e i g h t

a n d t h e h e ig h t o f t h e m e r c u r y in t h e e x p e r im e n ta l t u b e .

A f ina l s ign i f ican t f ea tu re o f POWER'S expe r ime n ts was , th a t in hi s en thus i asm

to der ive a quan t i ta t ive exp ress ion fo r the e las t ic i ty o f a i r , he lo s t s igh t o f i t s

w e ig ht , w h ic h l e d h im in a n o th e r e x p e r im e n t t o g iv e a n i n c o r re c t e x p l a n a t i o n f o r

the ac t ion o f the s iphon . H is exper im en ts as a who le show tha t he had on ly a l im-

i t e d a b i l i t y t o r e d u c e h i s e x p e r im e n t s i n to t h e t e r m s o f q u a n t i t a t i v e h y d r o s t a t i c s .

T h e s e t e n t a t i v e a n d i n c o n c lu s iv e e x p e r im e n t s o n t h e s p r in g o f a i r b r i n g t oan end POWER'S f i r s t se r ies o f exper im en ts , and h is in te res t in the sub jec t was

no t r e v ive d un t i l t660 , w hen he r ead the work o f ROBERT BOYLE.

VII . Boyle ' s F irs t Researches on Air Pressure: The Pneumatic Engine

A s I h a v e p r e v io u s ly p o in t e d o u t , BO Y L E w a s p r o b a b ly f a m i l i a r w i th t h e

Tor r ice l l ian exp er im en t f ro m the t ime o f i t s in t roduc t ion in to E ng lan d in 1647,

b u t i t w a s n o t u n t il t 6 5 8 t h a t h e b e g a n h is m o r e s y s t e m a t i c s t u d y o f t h e p h ys i c a l

a n d c h e m ic a l p r o p e r t ie s o f ai r. T h e g r e a t e s t s t im u lu s t o t h i s w o r k w a s t h e i n v e n -

t ion of the air p um p by OTTO VOI~GUERICKE in ab ou t t 654 , and BOYLE real ised th at

t h i s a p p a r a tu s c o u ld be ~ as e d f o r p e r f o r m in g e x p e r im e n t s in vacuo. I t i s no t ce r ta in

how BOYLE w a s in t r o d u c e d t o y o n GUERICKE'S a p p a r a tu s , '9 si n ce t h e l a t t e r ' s

b o o k w a s n o t p u b l i s h e d u n t i l t 6 7 2, b u t i t i s p r o b a b M - th a t h e w a s t o ld a b o u t i t

b y o n e o f h i s c or r e s po n d e n t s , w h o m ig h t h a v e s e e n t h e e x p e r im e n t s o r r e a d t h e

acco un t o f the p um p in SCHOTT'~ Mechanica hydraulico-pneumatica, which was

pub lis he d in 165 7. 8oAccord ing to BOYLE'S accoun t he had c on te mp la te d the evac ua-

t ion o f a vesse l w i th a suc t ion p um p p r io r to t6 58, bu t the success o f the Ge rm an

expe r ime n ts conv ince d h im to p rosec u te h i s own inves t iga t ions . 81

7~ Ib id .. p. to7 .

~8 Ibid., p . 116: While it w ould h ave bee n possible to derive a functiona l rela tion-sh ip between the me rcury height and the air volume, th is would have been comp letelybeyond Pow•R's ma them atical ab il i ties.

~9 OTTO vo ~ GUERICKE, Experimenta Nova (_ut vfcantur) Magdeburgica de 'Vacuo5patium a R. P. Gaspare Schotto. Amsterdam, t672.

80 CASPAR SCHOTT,Mechanica Hydrau. lico-Pneumat~ca, Wfirzburg, t657..81 ROBERT BOYLE, 1660, op::eit., Works, vo_l. 1, pp . 4 5.



Boyle ' s Law and the E las t ic i ty o f A i r 465

B y J a n u a r y 1 6 5 8 BOYLEhad wr i t ten to HARTLIB abo u t " t h e G e r m a n v a c u u m

a s of n o o r d in a r y b e a u ty " , 8 ~ a n d i n t h e s a m e y e a r h e e m p lo y e d RAL PH GREATOREX,

the L ondo n in s t rum en t ma ker , and ROBERT HOOKE, h is as s i s tan t a t O xfo rd ,t o c o f lS t ru c t a n a i r p u m p . T h e f i n a l d e s ig n a n d

c o n s t ru c t i on o f t h e a p p a r a t u s w e re m a i n l y t h e

work o f HOOKE, bu t GREATOREX m ay hav e been

respons ib le for dnqling- the p is t on cyl inder . 8a

BOYLE could h ave ga ined l i t t l e p rac t ica l in fo r -

m a r io n a b o u t t h e c o n s t r u c t i o n o f t h e p u m p f r o m

SCHOTT'S book. Inde ed , i t is pro bab le t ha t

HOOKE'S pump great ly exceeded voN GUERICKE'S

in e f f ic iency an d ~des ign , s ince the Ge rm an la te r

modif ied h is own design to conform to HOOKE'S,

th u s a c c o u n t in g f o r t h e s im i l a r i t y of e v e n s u p e r-

f i c i a l p o in t s o f c o n s t r u c t i o n b e tw e e n th e p u m p s

il lus trate d in BOYLE'S wo rk o r t66 0 an d VON

GUERICKE'S of 1672. s~

T h e r e w e r e tw o m a jo r d i f f er e n ce s b e tw e e n th e

G e r m a n a n d En g li s h p u m p s ; t h e G e r m a n p u m p

u s e d a l e v e r t o o p e r a t e t h e p i s to n a n d t h e e v a c u -

a t e d g lo b e h a d o n ly o n e o p e n in g , w h ic h w a s

a t ta che d to the pu m p ; wh i le ]~OYLE'S pu m p useda more e f f ic ien t r ack and p in ion fo r mov ing

th e p i s to n a n d t h e r e w a s a s e c o n d o p e nin g in to

the g lobe, wh ich enab led the in ser t ion o f ex -

p e r i m e n t a l o b j e c t s .

S inc e t h e r e a re m a n y a d e q u a t e d e s c r ip t i o n s

o f BOYLE'S a i r pu m p 85 o r " pn eu ma t ic eng ine! ', I

w i l l cons ider on ly i t s app l ica t ion to the exami-

nat i on of a ir ' s e la s t ic i ty . BOYLE'S de scr ip t ion of

t h e p u m p a n d n u m e ro u ~ c he m i c a l a n d p h y s i c al

a~ L e t te r f o rm SA~MUELHARTLIB o BOYLE,J a n u -ary , t658; Works, vol. 5, p. 27t.

8a HOOKE'S contr ibut ion to the construct ion and Fig.4.R.BoYLE, New Experiments Physico-

design , of BOYLE'S air pu mp has been d iscussed Mechanicall,London, *660, Works, vol.1,by , R. W A L L E R , Posthumous Works o] Hooke, London, Endp late Fig. I . BoYLE's air. pum p or

"pnetmaatic engine"

t705, pp, il l -- i v; R. T. GUNTHER, Early Science atOxford, vol. 6, Oxford , 1936, pp.. 8- -9 , 70---72; R.F.FULTON, Bibliography o[ the Honourable Robert Boyle, Second edition, Oxford, 1960,p . t l ; H . D . T UR N ER , Robe r t H ooke and Boy le ' s a ir .pump , Nature, a959, 184,PP. 395---397.

84 ~ee Figure 4. This a pp ara tus is very similar to th at Oil the title page of yo nGUERICKE'S wo rk. See J. R. PARTINGTON,History of Chemistry, vol. 2, t961, p. 516.

ss Good desc riptions of BOYLE'S air p u m p are t o.b e found in, R. BOYLE, Works,op,~ it. , vol. I , pp. 4 5; E .N . DA C. ANDRADE, Th e earl y his tory of the va cu ump u m p , Endeavour, t957, 16, pp. 2 9- -4 t; J. ]3. CONA~T, Harvard Ca.se Histories inExperiental Science, 2 vols. Ca mb ., Mass. 1950, vol. t, pp. t 64; G. WILSON, Relg$oChemici, London, 1862, pp. 193--218.



466 C. WEBSTER:

exp erim ents s6 us ing i t w ere publ is hed in Ox ford in t660, as Ne w E x pe r i m e n t s

Phys ico-Mechanical l , Touching the S pr in g of the Air . sT

As the t i t l e and i n t ro duc to ry exp er imen ts ind ica te , BOYLE was par t i c u la r lyconcerned wi th the e xam ina t ion o f the h ypo the s i s o f the sp r ing o f a i r, hav ing

once re pea ted . the proofs Of i ts weight .

Th a t h e w as s ti m u l a t ed t o ex am i n e t h e e l a s t ic i t y o f a i r b y t h e F ren ch ex P e r i -

men ts i s sugges ted a t the very beg inn ing o f the work , when he admi t ted tha t he

h ad b een i n d u ced t o s t u d y t h e To r r i ce l li an ex p e r i m en t b y "p e rce i v i n g b y l e t t e r s

f rom some o ther ingen ious persons a t Par i s , tha t severa l o f the Vi r tuos i there

were very in ten t upon th e ex ami na t ion o f the in te res t o f the a i r, in h inder ing

the de scent of the quick si lver" . Since he knew of PECQUET'S book, and quo ted

from i t in the second edi t ion of h is own work, i t i s poss ible tha t th is was an

i m p o r t an t "F ren ch " i n f l u en ce o n h i s co n cep t o f a i r p r e s s u re .The f i r s t par t o f the work was focussed on p rov ing tha t the a i r had the p ro -

per t i es o f weigh t and sp r ing . W eigh t was the p r im ary q ua l i ty o f a ir , and th i s

charac te r i s t i c was ded uced f rom PASCAL'S Pu y de D6me exper im en t , th e T or-

r ice l l i an exper imen t and by the d i rec t weigh ing o f a i r . He was no t sa t i s f i ed tha t

p rev ious t r i a ls had been su f f ic ien t ly accur a te ; he used method s s imi lar to those

of GALILEO and MERSENNE, bu t ac hieve d con sidera bly gre ater accu racy, f inding

th at wa ter eas 938 t imes as dense as a i r . 88

He was equa l ly conv inced o f the e las t i c i ty o f a i r, and he sough t a theo re t ica l

m o d e l w h i ch w o u l d ex p l a i n t h i s p h en o m en o n . H e f av o u red m o s t a m o d e l v e ry

l ike tha t p roposed b y POWER, excep t tha t he was undec ided w hethe r the co rpusc les

were suspended in an ae ther o r vo id . H is op in ion is quo ted in fu ll as Append ix 'V.

As the inves t iga t ions o f the phys ica l p roper t i es o f a i r p rogressed he incessan t ly

re fe r r ed to t h is t h eo ry o f el a t e r o r sp ri ng . H o w ev e r , h e w as u n d ec i d ed w h e t h e r

th i s rep resen ted the t rue s t ruc tu re o f a ir , s ince a i r was ab le to d i l a te wi tho u t

prior compress ion . 89 He pre sen ted DESCARTES' t h eo r y o f t h e s t ru c t u re o f ai r an d

no te d th a t i t was o f l i t t l e s ign i f icance wh at shape was sugges ted fo r the co rpusc les ,

s ince the i r p ressu re resu l ted f rom " the vehemen t ag i ta t ion . . . wh ich they rece ive

from the f lu id a ether . ' '9°

Whi le BoYi .E adop ted exp lana t ions o f phys ica l p rocesses by h i s "Mechan ica lo r Corpuscu la r Ph i losophy , he care fu l ly avo ided com mit me n t in the d i spu tes

abou t the u l t imate mechan ica l p r inc ip les . Thus he used the p len i s t and vacu is t

models o f a i r to i l lu s t ra te t i le phenomena" o f e last i c i ty , bu t he w as care fu l to

co n c lu d e t h a t i t w as p ro b ab l e t h a t n e i t h e r r ep re s en t ed t h e a i r ' s t r u e p h y s i ca l

cons t i tu t ion . Th is a t t i tud e he lps to exp la in the ind igna t ion which h e fe l t when

HOBBES accused h im o f in t roduc ing the vacu is t in te rp re ta t io n , and i t was perhap s

86 Th e v~trious exp er im en ts p erfo rm ed w ith BOYL]~'S pum p ha ve been discuss 6dbY G. WILSON,op. cir., pp. 2t9--228; J , R. PARTINGTON., 961, op. cit., pp. 520--5281.

87 ROBER~ BOYLE, Ne w Experim enIs ]ahysico-Mechanicall, Touching the Spring

o/ the Air, Oxfo rd, t 660. - - Ne w Exp erime nts Physico-Mechaniea[, Touch ing the A ir .The Second Edition. Whereunto is added A Defence o/ the Authors Explication of theExpe riments, A ga inst the Obiections O/Franciscus Linus, An d, Thoma s Hobbes, Oxford,i 662.

s8 R. BOYLE,, 1"660, op. ci r. ; Works, vol. t , pp. t2--13, 55--56.s~ Ibid., P.'9.90 Ib id. , p. 8.



Boyle ' s Law-and the E las t ic i ty o f A ir 467

th i s m i s in t e r p r e t a t i o n w h ic h p r o v o k e d th e p a th o lo g i c a l l y im p a r t i a l BOYLE to

wr i te a s t ing ing c r i t i c i sm o f HOBBES in the second e d i t io n o f the New Experiments

Physico-Mechanical in t662 .H e d e m o n s t r a t e d t h e e l a s t i c i t y o f ai r b y ROBERVA L'S c a r p - b l a d d e r e x p e r im e n t ,

wh ich h ad o r ig ina l ly been me n t io ned to h i m by HARTLIB in t648 , 91 He the n

s h o w e d th a t a s im i l a r r e su l t e n s u e d o f t h e b l a d d e r w a s p l a c e d i n a n e x h a u s t e d

g lass g lobe . The e las t ic i ty o f a i r was in f luenced by tempera tu re as wel l as ex te rna l

p r e s s u r e . T h i s w a s s h o w n b y m o v in g a p a r t i a l l y i n f l a t e d b l a d d e r n e a r e r a n d

f u r th e r f r o m a f ir e. W h e n th e b l a d d e r w a s b r o u g h t n e a r e r t o t h e f i r e " t h e e l a s ti c a l

p o w e r o f t h e s a m e q u a n t i t y o f a i r m a y b e a s w e l l i n c r e a s e d b y t h e a g i t a t i o n o f

th e a e r i a l p a r t i c l e s " . W h e n th e b l a d d e r w a s m o v e d a w a y f r o m th e fi re , t h e

b l a d d e r d e f l a t e d ; b u t i f i t w a s t a k e n t o o n e a r , i t b u r s t . 92

I t h a s o f t e n b e e n o v e r lo o k e d th a t BOY LE w a s n o t o n ly c o n c e r n e d t o g iv e aq u a l i t a t i v e d e m o n s t r a t i o n o f a i r ' s e l a s t i c i t y , b u t h e a l s o w i s h e d to r e d u c e t h i s

p h e n o m e n o n to a q u a n t i t a t i v e l a w . A s e a r ly as E x p e r im e n t 793 h e t u r n e d t o t h i s

p r o b l e m , w h e n h e e x a m in e d t h e e x t e n t t o w h ic h a v o lu m e o f a i r w o u ld e x p a n d

w h e n s u b j e c t e d t o r e d u c e d p r e s s u r e .

A smal l g lass tube , 6 o r 7 inches long , was sea led a t one end a nd a par ch me n t

c a l i b r a t e d s c a l e w a s a t t a c h e d t o t h e s i d e . T h e s c a l e e n d e d j u s t b e lo w th e a p e x

o f t h e t u b e , w h ic h w a s e x p a n d e d in to a s m a l l gl a ss glo be . T h e a p p a r a tu s w a s

f i l l e d w i th w a te r , e x c e p t f o r th i s g lob e , w h ic h c o n t a in e d a n a i r b u b b le . T h e o p e n

e n d o f t h e t u b e w a s im m e r s e d i n a s m a l l d is h o f w a te r , a n d t h e w h o le a p p a r a tu s

w a s p l a c e d i n t h e g lo b e o f t h e e v a c u a t io n a p p a r a tu s .A s t h e g lo b e w a s e x h a u s t e d t h e a i r b u b b le e x p a n d e d u n t i l i t f i l l e d t h e w h o le

tu ] 3 e . I n t h e n e x t e x p e r im e n t h e f o u n d th a t a i r h a d a n e v e n g r e a t e r c a p a c i t 9 f o r

e x p a n s io n a n d i t c o u ld i nc r e a se i t s v o lu m e i t s v o lu m e b y 2 5 2 tim e s . T h i s c o n f i r m e d

MERSENI;E 'S exp er im en ts on the r a re fa c t ion o f a ir .

A m o r e s a t i s f a c to r y m e th o d f o r s t u d y in g t h e q u a n t i t a t i v e a s p e c t o f t h e e l a s ti -

c i* y o f ai r w a s d e s c r ib e d i n E x p e r im e n t 17. T h e T o r r i c el l i a n e x p e r im e n t w a s s e t

u p , a n d t h e d i s h, c o n t a in in g t h e r e s id ua l m e r c u r y a n d t h e l o w e r e n d o f t h e T o r -

r ice l l ian tube , was enc losed wi th the g lass g lobe o f the exhaus t ion appara tus .

BOY LE p o in t e d o u t t h a t t h e m e r c u r y w a s n o w c u t o f f f r o m th e w e ig h t o f th e

a t m o s p h e r e a n d m u s t b e s u p p o r t e d b y t h e e l a s ti c i ty r a t h e r t h a n t h e w e i g h t o f

the a i r .

. . . u pon which closure there appeare d not a ny change in the height of the m ercur ialcy l inder , no more tha n if the in terposed g lass receiver d id not h inder the im med iatepressure of the ambient a tmosphere upon the inclosed air ; which hereby appearesto bear upon the mercury , ra ther by v ir tue of i ts spr ing than of i ts weight; s incei ts weight cannot be supposed to amount to above two or three ounces , which isinconsiderable in compar ison of such a cy l inder of mercury as i t would keep f romsubs iding , 94

T h e h y p o t h e s i s t h a t t h e m e r c u r y i n t h e T o r r ic e ll i an t u b e w a s. n o w s u p p o r t e d

b y th e e l a s t i c i t y r a th e r t h a n t h e s p r in g o f a i r , w a s a n e s s e n t i a l a s s u m p t io n f o r.....h i s f ol lo w ii ig a t t e m p t t o d e t e c t t h e re l a t i o n s h ip b e tw e e n th e e l a s t i c i t y a n d v o lu m e

9x Se~ foo tno te 4 5.92 Ibid., p. 13.9z Ibi d., p. t4.9a Ibi d., p. 22.



468 C. WEBSTER:

o f a i r. B OY LE sa w t h a t t h e 2 9 i n c h e s o f m e r c u r y i n t h e T o r r i c e l l i a n t u b e c o u l d

n o t n o w b e s u p p o r t e d b y t h e weight o/ a column o /a ir s i n c e it w a s e f f e c t i v e l y c u t

o ff f r o m t h e a t m o s p h e r e b y t h e s e a l e d g l as s gl o be . T h e m e r c u r y w a s n o w s u p -p o r t e d b y t h e r e s i s t a n c e o f t h e p a r t i c l e s of a i r .

A s i m i l a r c o n c l u s i o n h a d p r e v i o u s l y b e e n r e a c h e d b y T OR RIC EL LI, w h o h a d

b e e n a s k e d b y R lC C195 t o e x p l a i n t h e s u s p e n s io n o f t h e m e r c u r y c y l i n d e r u n d e r

s i m i l a r c ir c u m s t a n c e s ; h e h a d r e p l i e d t h a t t h e l o w e s t l a y e r s o f a i r w er e c o m p r e s s e d

b y t h e u p p e r , a n d t h i s d e gr e e of c o m p r e s s i o n w a s u n i n f l u e n c e d b y p l a c i n g t h e

a i r in a n e n c l o s e d p l a c e :

. . . b u t i f t h e a i r t h a t y o u i n c l u d e is m o r e r a r e f i e d t h a n t h e e x t e r n a l a i r , t h e n t h e

s u s p e n d e d m e t a l w i l l d e s c e n d b y tl~e p r o p e r a m o u n t ; i f n o w i t w e r e i n f i n i t e l y r a r e fi e d ,

i .e ., a v a c u u m , t h e n t h e m e t a l w o u l d d e s c e n d a l l t i l e w a y , p r o v i d e d t h a t t h e e n c l o s e d

space w er e ab l e t o t ak e i t . 9~

H o w e v e r , t h e r e i s n o e v i d e n c e t h a t TORRICELLI m a d e a n y e x p e r i m e n t a l c o n -

f i r m a t i o n o f t h i s i m p o r t a n t h y p o t h e s i s . I n d e e d , t h e r e i s e v i d e n c e t h a t h e a v o i d e d

f u r t h e r d e v e l o p m e n t o f t h i s w o r k , p e r h a p s i n d e f er e n c e t o r e li g io u s d i s a p p r o v a l

o f u n o r t h o d o x t e n d e n c ie s . A l s o , W h il e h e a p p r e c i a t e d t h e . g e n e r a l n a t u r e o f t h e

a i r ' s e l a s t i c i t y , h e w a s n o t s u r e t h a t d e n s i t y a l o n e W a s n o t r e s p o n s i b l e f o r c h a n g e s

i n p r e s s ur e . T h u s , r e d u c t i o n o f a i r p r e s s u r e a t h i g h a l t i t u d e s w a s d u e to i t s g r e a t e r

" p u r i t y " , a n d a t l o w a l t i t u d e s h e a t c a u s e d a i r t o b e " m o r e s u b t l e a n d l i g h t " .

I t w a s l e f t f o r PA SC AL t O e x a m i n e t h e i n f l u e n c e o f a l t i t u d e o n t h e h e i g h t o f

t h e m e r c u r y c o l u m n a n d f or BOYLE t o r a r e f y a ir w i t h hi s v a c u u m p u m p . M o r et h a n t h i s , h e h o p e d t h a t h e m i g h t d e r i v e a l a w f r o m t h e r e s u l ts , w h i c h w o u l d

r e l a t e t h e d e n s i t y o f t h e e n c lo s e d a i r to i t s e l a s t ic i t y . T h e f o r m e r c o u l d b e e s t i m a t e d

f r o m t h e g t r o k e of t h e p u m p , s in c e t h e d i m e n s i o n s o f th e p i s t o n c y l i n d e r w e re

a c c u r a t e l y k n o w n ; t h e l a t t e r w a s m e a s u r e d d i r e c t l y . a s t h e h e i g h t o f t h e m e r c u r y

c o l u m n .

T h i s e x p e r i m e n t w a s c o n d u c t e d i n t h e p r e s e n c e o f W R E N , W A LL IS a n d WARD,

t h r e e of t h e n a t i o n 's m o s t p r g m i n e n t m a t h e m a t i c i a n s , a n d t h e y f o u n d t h a t t h e

d e s c e n t o f m e r c u r y d e c r e a s e d w i t h t h e i n c r e a s in g e x h a u s t i o n .

W e f o r m e r l y m e n t i o n e d , t h a t t h e q u i c k s i l v e r d i d n o t , i n i t a d e s c e n t , fM1 a s m u c h

a t a t ime , a f t e r t he tw o o r t h r ee f i r s t exsuc t ions o f t he a i r , a s a t t he be g inn ing . Fo r ,h a v i n g m a r k e d i t s s e v e r a l s t a g e s u p o n t h e t u b e , w e f o u n d , t h a t a t t h e f i r s t s u c k

a n d w h e n t h e v e s s e lt d e s c e n d e d a n i n ch a n d 3 a n d a t t h e s e c o n d a n i n c h a n d s ,"8,

w a s a l m o s t e m p t i e d , i t w o u l d s c a r c e a t o n e e x s u c t i o n b e d r a w n d o w n a b o v e t h e

b r e a d t h o f a b a r le y - c o r n :97~

H e c o n c l u d e d t h a t :

W e c o u l d n o t h i t h e r t o m a k e o b s e r v a t i o n s a c c u r a t e e n o u g h c o n c e r n i n g t h e m e a s u r e s

o f th e q u i c k s i l v e r ' s d e s c e n t , to r e d u c e t h e m t o a n y h y p o t h e s i s , y e t w o u l d w e n o td i s c o u r a g e a n y f r o m a t t e m p t i n g i t, s in c e, i f i t c o u l d b e r e d u c e d t o a c e r t a i n t y , i t i s

p r o b a b l e , t h a t t h e d i s c o v e r y w o u l d n o t b e u n u s e f ul , g8

~5 L et te r fro m RlCCI, tO TORRICELLI, t8 Jun e, . t64 4; TORRICELLI Opere, op . c i t . ,

vol . 3, pp . 21 22.96 L e tt e r fro m TORRICELLI I:O RlCCI, 28 J.une 1644, 01)ere, vo l . 3 , pp . 198 - -20 1 .

The qu o ta t i o n i s t a ken . f ro m KNOWLES MIDDLETON t963 op~ cit. ( see foo tno te t ) , p . 23.97 R. :BOYLE, 1660, op . ci t., Works, voh 1, p. 23.

9s Ib id ., p. 23. -_



• B oy l e ' s La w and t he E l a s t i c i t y o f A i r 469

T h i s f a il u r e to o b t a i n a s a t i s f a c t o r y h y p o t h e s i s w a s n o t s u r p r i s in g , e v e n g i v e n

t h e h e l p of p r o m i n e n t m a t h e m a t i c i a n s . C o m p a r i s o n s b e t w e e n t h e r e a d i n g s w o u l d

b e r e n d e r e d u s el e ss , s i n c e t h e l e a k a g e o f t h e c o n t M n e r i n c r e a s e d a s i t w a s p r o g r e s -s i v e l y e x h a u s t e d l I n a d d i t i o n , t h e T o r r i c e ll i a n t u b e w a s n o t c a l ib r a t e d , a n d

w h e n t h e m e r c u r y l e v e l h a d f a l le n b e l o w t h e l e v e l o f t h e l i p o f t h e g l o b e , t h e

l e v e l w a s g u e s s e d b y e y e . 99

I t w a s r e a l is e d t h a t l e a k a g e w a s i n s ig n i f i c a n t d u r i n g t h e f i rs t S t r ok e s o f t h e

p u m p , t h e r e f o r e h e r e p e a t e d h i s e x p e r i m e n t , h o p i n g t o c o m p a r e t h e r e s u l t s f o r

t h e i n i ti a l e x s u c t i o n s o f g l o b e s o f d i f f e r e n t c a p a c i t i es . T h i s , h e h o p e d , m i g h t l e a d

t o a • s a t i s f a c t o r y h y p o t h e s i s .\

Bu t o n th i s occas ion, I hold i t no t uni i t to g ive YOUr Lor dship not ice , th a t Il lope.d f rom the descen t of the quicks i lver in the tube , up on th e f i r s t suck, to der ive

t h i s advan t age ; t ha t I shou l d t hence be enab l ed t o g i ve a nea r e r gues s a t t he p ro -por t ion of force be t wix t the pressure o f the a i r (according to i t s var ious s ta tes , ast o dens i t y and r a r e f ac ti on ) and t he g r av i t y o f qu i cks i lve r , t han h i t he r t o h a t h beendone.100

T h i s m e t h o d w o u l d h a v e p r o v e d s a t i s f a c t o r y h a d h e c h o s e n g ro b es o f s u i ta b l e

s i ze s , bu t h i s f i r s t C ho ice : w as a g l obe w hi ch he l d l e s s t han ~ qu a r t o f l i qu i d , o r

l es s t h a n 6 9 c u b i c i n c h e s o f a ir . T h u s , t h e p i s t o n w a s c a p a b l e o f w i t h d r a w i n g 9 9

c u b i c i n c he s i n o n e s t r o k e , a n d a l m o s t c o m p l e t e l y e x h a u s t i n g t h e g l o be . H o w e v e r ,

sucl;1 a g r ea t r e du c t i o n i n p r e s su re w o u l d cau se cons i d e r ab l e l eak age , and B O YLE

f o u n d t h a t t h e m e r c u r y •fell t o 8 { o r 9 { i n c he s . T h e r e f o r e , t h i s r e s u l t c o u l d n o t

b e c o m p a r e d w i t h t h e f i r s t s t r o k e s i n h i s f o r m e r e x p e r i m e n t . H e a l s o s u g g e s t e dt h a t ' t h e u s e o f a s m a l t g l o b e i n t r o d u c e d o t h e r d i f fi c u lt ie s . T h e r e s i d u a l m e r c u r y

v o l u m e d e c r e a s e d a s t h a t i n t h e t u b e f e l l ; h e s u g g e s t e d t h a t t h i s w o u l d i n f l u e n c e

t h e a c c u r a c y o f t h e p r e s su r e d e t e r m i n a t i o n . F u r t h e r , tl~e s u b s e q u e n t v o l u m e s

o f a ir e x t r a c t e d f r o m t h e g l ob e w o u l d b e m o r e r a r e fi e d , a n d c o n s e q u e n t l y i t

w o u l d n o t b e c o m p a r a b l e t o a n e q u a l v o l u m e o f a i r a t . a t m o s p h e r ic p r e s s u r e .

~ W i t h t h e s e d i f f i c u l t i e s i n m i n d , h e c o n c l u d e d :

B ec au se o f t hese ( I s a y and some o t he r d if fi cul ti e s, t h a t r equ i re mo re sk il l i nma t h ema t i c s t han • I p r e t end t o , an d much• m or e l ei su r e t ha n m y p re sen t occas ionswould a l low me, I was wi ll ing to refer the n icer cons idera t ions of th i s m at t er to som e

of ou r l ea rned and accura t e ma t hema t i c i ans , t h i nk i ng i t enough fo r me t o havegiven the .h in t a l re ad y sugges ted , l°x

T h i s c o n f e s s i o n s h o u l d n o t b e r e a d a s i n d i c a t i n g B O YL E 'S w e a k n e s s a t m a t h e -

m a t i cs , a s m a n y c o m m e n t a t o r s 1°~ h a v e u n d e r s t o o d i t, b u t a n i n d i c a t i o n o f t h e

99 Ib id ., p. 231100 Ibid . ( p . 24 . BOYLE gave suf f ic ient info rma t ion for i t to be es tabl i shed th a t

t he r e w as l i t tl e l eakage d ur i ng t he f i rs t f ew st rokes o f t he pu mp . The g l as s g l ob e

of the a pp ara t us he ld 30 qua r t s of l iquid , or abo ut t .2 cubic fee t . Since i t was ap-p rox i m a t e l y sphe ri cal , i t s d i ame t e r w as ab ou t 8 inches . The p i s t on ' cy l i nde r w as14 i nches l ong and 3 inches il l d i ame t e r and it s. ma x i m um capac i t y w as t he r e fo re

99 cubic inches. A s ingle s t roke of the p i s ton was able to exh aus t a bo ut 4 .8% of thesphere ' s con tent of a ir . At the f i r s t s t roke th e m erc ury fel l f rom 27 to 25 ~ inches,%-vhichwas a fa l l of 5 .1%. Had there been leakage , the mercury would have fa l len less .

~o~ Ib id ., p. 2 4.

102 R. T. GUNTHER,Early Science in Oxford, Vol. 6, Oxford, 1930, p. 73. GUNTHERat t r ibutes the fa i lure of BOYLE~Sw ork t o h i s l ack o f ma t h ema t i ca l ab i l i ty com bi nedwi th weak eyes ight .



4 7 0 C . W E B S T E R :

i n h e r e n t d i ff i cu l ti e s o f t h i s p a r t i c u l a r e x p e r im e n t f o r d e t e r m in in g t h e r e l a t i o n s h ip

b e tw e e n th e p r e s s u r e a n d v o lu m e o f a ir . T h e im p o r t a n c e o f t h e s e e x p e r im e n t s

a r e t h a t t h e y r e p r e s e n t BO Y L E ' S f i r s t s y s t e m a t i c a t t e m p t t o d e t e r m in e t h e l a wr e l a t i n g th e tw o d e p e n d e n t v a r i a bl e s , t h e " s p r in g " o f a i r ( w h ic h h e n o w t e r m s

i t s " p ress u re" ) and i t s dens i ty . 1°3

Al though BOYLE'S in i t ia l a t tempt to de te rmine the law was a f a i lu re , the

exp er im en t i s o f the g rea t es t .in te res t as an i l lu s t r a t ion o f BOYLE'S app roa ch to

a n e x p e r im e n ta l p r o b l e m . H e h a d c l e a r ly in h is m in d t h e g o a l of t h e e x p e r im e n t

wh ich was to ob ta in a tab le wh ich wou ld compare the d i f f e ren t dens i t ies and

r e l a t e d p r e s s ur e s o f a ir . T h i s a m b i t i o n w a s t h w a r t e d b y t h e t e c h n ic a l im p e r f e c -

t i o n s of t h e a p p a r a tu s , a n d i t is i n t e r e s t i ng t h a t n e i t h e r h e n o r hi s m a th e m a t i c a l

co l league were wi l l ing to r i sk the fo rmula t ion o f a hypo thes is on the in i t ia l r esu l t s

o f t h e i r f i rs t e x p e r im e n t , a l t h o u g h w e n o w r e a li s e t h a t t h e s e i n d i c a t e d a p r o -p o r t i o n a l i t y b e tw e e n d e n s i t y a n d p r e s s u r e .

BOY LE th e n S o ug h t t o a v o id t h e f o r m e r e x p e r im e n ta l e r r o rs , b u t u n f o r tu n a t e ly

he chose an exped ien t wh ich increased the r i sk o f leakage and in t roduced fu r the r

c o m p l i c a t i o n s W h ic h r e d u c e d t h e v a i i d i t y o f c o m p a r i s o n s w i th t h e f o r m e r e x -

p e r i m e n t .

The pub l ica t ion o f ]3OYLE'S expe r ime n ts in t660 led to g re a t in te re s t in the

hyp o th es is o f the weigh t and sp r ing o f a i r. LINUS and HOBBES lo4 p roduced p ro -

t r a c t e d r e f u t a t i o n s o f h is e x p l a n a t i o n s , w h ic h h a d t h e v a lu a b l e f u n c t io n o f s t im u -

l a t i n g BOY LE to a d d a l e n g th y A p p e n d ix t o t h e f o r m e r w o rk , a n d t o e m b a r k o n

f u r th e r e x p e r im e n t s . I t a ls o s t im u la t e d v a r io u s a u th o r s t o e n g a g e in t h i s f r u it f u lexp er im en ta l s tudy . These inc luded a la rge comm it tee 105 o f the n ewly in s t i t u te d

R oy al Society , GEORGE SINCLAIR in Scotlan d , and POWER and TOWNELEY in

th e n o r th o f E n g la n d .

V I I I . P o w e r a n d T o w n e l e y : T h e D i r e c t M e a s u r e m e n t o f t h e E l a s t i c it y o f A i r

I t h a s p r e v io u s ly b e e n m e n t io n e d t h a t R ICH ARD T OW N EL EY w a s t o s o m e

e x te n t i n v o lv e d i n P OW ER'S e x p e r im e n t s o f t 6 53 , a n d w h e n th e s e e x p e r im e n t s

w e r e re s u m e d in t 6 6 0 , i t w a s u p o n th e i n i t a t i v e o f b o th m e n .

I h a v e a l r e a d y g iv e n t h e m a jo r b io g r a p h ic a l d e t a i l s b y P OW ER l°6, b u t h a v eon ly ma de inc iden ta l r e f e rence to RICHARD TOWNELEY.

TOWNELEY'S name i s n o t i n s ig n i fi c a n t i n t h e h i s to r y o f s e v e n t e e n th c e n tu r y

sc ience , fo r he was assoc ia ted wi th the inven t ion o f the r a in -gauge , the im prov e-

me n t and pub l ic a t ion o f the de ta i l s o f GASCOIGNE'S mic rom eter , meteo ro log ic a l

1o8 These exper imen ts co r rec t the m isconcep t ion tha t BOYLE made no a t tem ptat a q ua nti tat ive esti ma tion of the Spring of air during his initial wor k in 1658 and 1659.

10~ FRANCISCUS LI NUS, Tractatus de corporum inseparabi'l~tate, London, t66t . - -THOMAS HOBBES, Dialogus physicus de natura aeris, London, t661.

105 On Jan ua ry t6 t h t660/61 , the Society appo in ted a comm ittee to s tud y the

Torricellian experiment. This consisted of BALL,-BROuNcKER,.BOYLE;'CLARKE,HILL;2{EILE, MORAY, ROOKE and WREN. T. BIRCH, 1756/57, op. Cit, vol. % p. t2.106 For furt her details of HENRY POWER'S life and work, see m y M. Sc. Disserta -

t ion "The Sc ien t i f ic Work o f Henry Power , M.D." London Un iver s i ty L ib ra ry :also T. COWLES, Dr. He nr y Power, Disciple of S ir Th om as Browne, Isis, 1933/34,20, pp . 344--366; J . W . CLAY, Dr. He nry Power of New Hall , F . R. S ., Hal i /azAntiq uaria n Society, papers, reports, t917 , pp . 1- -3 t . '



Boyle ' s Law and the E las t ic i ty o f A i r 471

reco rds and the sugge s t ion o f the hy po thes is , w h ich has beco me kno wn as BOYLE'S

L a w . T h e r e h a s ,. h o w e v e r , b e e n a n o t i c e a b l e l a c k o f b io g r a p h ic a l i n f o r m a t io n

a b o u t h i m , a n d h e h a s be e n b o t h p l a c e d i n t h e w r o n g c e n t u r y a n d c o n fu s e d w i t hhis uncle, CHRISTOPrlER TOW~ELEY of C arr an d Moo rhiles (16 o3 --t 67 4). ~°7

I w i l l the re fo re inc lude a f ew b iog rap h ica l de ta i l s in o rder to c la r i fy the

pos i t ion o f th i s my s te r i ous f igu re o f seve n tee n th cer~ tu ry sc ience , l°s The TOWNE-

LEY f a m i ly w e re im p o r t a n t l a n d o w n e r s i n S o u th L a n c a s h i r e , a n d t h e y t r a c e d

the i r descen t to an ecc les ias t ical dean o f Wha l ley , two cen tu r ies befo re the N orm an

Conques t . The i r ch ie f sea t was a t Towneley , near Burn ley . RlCr lARD TOWNELEY

(ToWNLEY) was b or n in 1629 an d w as th e elde st son o f CHARLES TOWNELEY,

wh o wa s kille d a t t he ba tt le of M ars ton Mo or in t644. WILLIAM GASCOIC-NE, a

f r iend o f the TOWNELEY fam i ly a n d phys ic i s t was k i l led in the nex t year . The

Roy al i s t and Catho l ic sy mp ath i es o f hi s f ami ly , as wel l as a r e t i r ing "d ispos it ion ,m a y e x p la in w h y RICHA RD e n te r e d l i t t l e i n to p u b l i c a f f ai r s a n d a v o id e d b e c o m in g

a m e m b e r o f t h e R o y a l S o c ie ty .

H e m ar ri ed MARGARET PASTON,1°9 da ug ht er of CLEMENT PASTON of Ba rn ing -

h a m , N o r f olk , w h o w a s f r o m th e f a m o u s N o r f o lk f a m i ly w h o s e l e tt e r s p r o v id e

in d i sp e n s ibl e e v id e n c e a b o u t t h e s o c i al h i s t o r y o f E n g la n d i n t h e f i f t e e n th a n d

s ix te en th cen tu r ies . RICHARD l ived a t No eton , n ear L inco ln , and a t Tow neley ,

w h e r e h e d e v o te d h im s e l f t o t h e s t u d y o f s c ie n c e a n d m a th e m a t i c s , l e a v in g t h e

m a n a g e m e n t o f h i s e s t a t e s t o h i s y o u n g e r b r o th e r , CHA RL ES (16~t--=t 7t 1). CHAR-

LES, an d an oth er B rother , JbHN ( i630 ?- -16 78) , ass is t ed RICHARD in h is scien t if ic

w o r k . A l th o u g h h e w a s n o t e d u c a t e d a t a U n iv e r s i t y , h e h a d a s o u n d u n d e r -

s t a n d in g o f L a t in a n d h e w a s f a m i l i a r w i th t h e m a jo r a c t i v i t i e s i n m a n y b r a n c h e s

o f n a tu r a l p h i l o so p h y , n ° H e a d d e d t o t h e l i b r a r y a t T o w n e le y , w h ic h w a s a l r e a d y

o n e of t h e f i n e s t p r iv a t e l i b r a ri e s i n t h e n o r th o f E n g la n d b y t h e b e g in n in g o f

t h e s e v e n t e e n t h c e n t u r y .

His sc ien t i fic in te res t s w ere ve ry s imi la r to tho se o f POWER, and the l a t te r

was bo th phys ic ian to the TOWNELEY fam i ly and co l lab o ra to r in sc ien t i f ic ac t i -

v i ti e s, b e tw e e n t6 53 a n d t 6 6 4. Bo th m e n w e r e d e e p ly i n f lu e n c e d b y t h e w r i t i n g s

of DESCARTES as well as t he En glish au th ors , BOYLE, WILLIS an d HENRY MORE.

102 CHRISTOPHER TOEVNELEY wa s a ce le bra te d an ti qu ar ia n.10s Info rm atio n ab ou t RICHARD TOWNELEY and his fam ily is sca ttere d thro ugh

many works. These include; -- CTIARLESLEIGH~ The Na tura l H i s to ry o / Laneashre , •Cheshire; and the Peak, i~¢_Derbyshire, Oxford , t 700, pp. 17--2 6. --- RALPH TttORESBY,Ducatus Leodlens is , Leeds, 17t5. - - J . HUNTER ed. The Dia ry o f Ra lph Thoresby

F . R . S . , 1677- -172g , 2 vols., London, 1830; Letters o/ Em in en t 2¥[en addressed toRa lph Thoresby , 2 Vols., Londo n, I832. - - THOMAS D. ~THITTAKER,A n H i s t o r y o [

the Original ,Parish of Whalley, Bla ckbu rn, 1801. -- F. R. RAINES, ed., The v is i ta t ion

o[ the Co unty Pal atin e o[ I~ancaster, made i n the year 16'64/65 b y Sir W ill ia m D ugdale,

Ch eth am Society Publicatio ns, vol. 88, Manchester , 1873, pp. 304--307. - - \V. T.LANCASTER, Letters addressed to Ra lph Thoresb y ~:. R. S . , Thoresby Society , Leeds ,

t912.109 The Pas ton Le t te r s A . D . 1~22- -1509 , 6 vols., ed. JAMES GAIRDNER, Lo nd on,t 9O4.

110 ]-~ICHARD ToWNEL EY'S m an us cri pt "S om e sho rt consi derat ions upp on Mr.Ho oke 's a t te m pt for ye Explica t ion o :f ye Ex pt . o f wat ers ascent in to small GlasseCanes ," is preserved in Yale Un ivers i ty Libra ry . An ap pended note by R. T. GUNTHERwrongly attr ibutes the work to CHRISTOPHERTO'WNELEY.



47,2 C. WEBSTER:

T h e i r c o l l a b o r a t i o n w a s p r o b a b l y h i n d e r e d w h e n POWER m o v e d t o W a k e f i e l d

i n i6 6 4 ; t h i s w a s ' f o l l o w e d b y i n t e r m i t t e n t i l lh e a l th , a n d h e d i e d - i n 1 6 68 .

T o w n e l e y H a l l w a g t o s o m e e x t e n t t h e f o c u s o f s i e n ti f ic a c t i v i t y i n t h e n o r t ho f En g l an d ; w r i t i ngs o f JER EMIA H H OR I~OC KS an d W l U aA ~ G ASCO IG NE pas sed

i n t o R IC HA RD TO WN E! , I~ / S hand s , an d he w a s v i s i t ed b y m a n y i n t e ll eC tua l s .

D u r i n g t h e l a s t y e a r s o f h i s l if e h e l i v e d a t Y o r k a n d h e d i e d t h e r e o n 2 2 n d

J a n u a r y , t 706/7.

POWER and TOWNELEY read BOYLE'S Ne w Exper imen t s Phys i co -Mechan ica l l

i n t h e y e a r o f i t s p u b l i c a t i o n , a n d t h i s r e s u l t e d i n t h e i r r e t u r n i n g t o t h e s t u d y

o f a i r p r e s s u r e a n d P a r t i c u l a r l y t o t h e i n v e s t i g a t i o n o f t ti e e l a s t ic i t y o f ai r w h i c h

t h e y h a d s o e f f e ct i v e ly d e m o n s t r a t e d i n t6 5 3 .

T h e y n o w u n d e r t o o k a s e c o nd s er ie s o f e x p e r i m e n t s w h i c h w e r e p e r f o rm e d

a t T o w n e l e y H a l ! in t 6 6 0 a n d t 6 6 t . P OW E R w r o t e a n a c c o u n t o f t h e s e e x p e r i-

m e n t s i n t h e e a r l y s u m m e r o f t 6 6 1 , e n t i t l e d :

Addit ional Experiments made at Townley Hal l , in the years 1660 and 1661, bythe advice and assistance of that Heroick and Worthy Gentleman, RICHARD TOWNLEY,EsQr. and t hose Inge nious Gentlemen Mr. JOHN, and CHARLES TOWNLEY, and Nfr.GEORGE KEMP.

T h i s w a s e v e n t u a l l y p r i n t e d i n th e s e c o n d p a r t o f h i s E x p e r i m e n t a l P h i l-

oso phy , i n t 663. 111 Th e a cco un t be gan by eu l og i s i ng B O YLE'S w ork .

The l a s t yea r , ' 1660 , came ou t t ha t exce ll en t Trac t a t e o f Experiments of Esqr .Boyle's, w i t h h i s P . neumat i ca l Eng i n , o r A yr -pu mp, i nven t ed , and pub l i shed b y h i m ,w here i n he has by v i r t ue o f t ha t r a r e C on t r ivance , o u t done a ll t ha t eve r poss i b l ycou l d be pe r fo rmed by our l a t e Mercuria l a n d Experimental Phi l osophe r s : A nd ,i ndeed , t o g i ve a t r ue and dese rved . C ha rac t e r o f t ha t w o r t hy Prod uc t i on o f h is ,I must needs say , I never read any such Trac ta te in a l l my l i fe , where in a l l th ingsa r e so cu r i ous ly and c r i ti ca l ly hand l ed , t he E xpe r i me n t s so j ud i c i ousl y and accura t e l yt r ied , and so candidly and in te l l ig ib ly de l ivered. I no sooner read i t , but rubbed upa ll my o l d do rma n t N o t i ons , and gave me a f r e sh v i ew o ! a ll m y fo rmer , and a l mos tforgot ten , Mercuria l Exper i men t s . N ay , i t had n o t t h a t e f f ec t one l y on me , b u tl i kew i se i t exc i t ed and s t i r r ' d up t he nob l e sou l o f m y eve r hono ured Fr i end , Mr .Townley, t oge t he r w i t h me , t o a t t e mp t t hese fo l low i ng Expe r i men t s . n2

P OW E R'S a c c o u n t o f t h e s e e x p e r i m e n t s h a d f e a t u r e s i n c o m m o n w i t h h i s

p r e v i o u s t r a c t o f t6 5 3 . T h e w o r k w a s i n t h e f o r m o f a se ri es o f e x p e r i m e n t s , w h i c h

w e r e d e s c r i b e d b ri e fl y l a n d i n c e r t a i n c a se s i n c o m p l e t e l y . A g a i n , t h e e l a s t i c i t y

o f a i r Wa s t h e s u b j e c t w h i c h r e c e i v e d g r e a t e s t e m p h a s i s , b u t t h e r e w a s l es s d i s-

c u s s io n o f t h e v a c u i s t - p l e n i s t c o n t r o v e r s y t h a n i n t h e f o r m e r w o r k . A s b e fo r e ,

111 HEN RY P(D'vVER,Experimental Philosophy, Lon don, 1663, pp . 121- -137 . Ama nus cr ip t vers ion of the sam e exper iments , hav ing the sam e t it l e, i s in the Br i t i shMuseum, Sloane MS 1393, f f . 154- -167. - - Ti le i t a l i cs and capi ta l l e t t e r s in the quo-t a t i on a r e a s w r i t t en by POWER . I have p r ev i ous l y po i n t ed ou t t h a t t he p r e sen t a t i onof t he t i tl e i n t h i s f o rm w as p ro bab l y t he cause o f B O YLE a t t r i bu t i ng t he expe r i men t sto TOWNELEY Rich ard T own eley and Boyle ' s Law, Nature, 1963, 197, pp. 226 --22 8. - -

POWER wro te two other sh or t t rac t s on a i r pressure be tw een 1660 and 1663. Th efirst, " A Con futa t ion of th i s F unic ular H ypo thes i s of Linus ; by He nr y Power , M a e 'Dr" "was publ i shed in Experimental Philosophy, pp. 138- -142. Ti le second, "Phys ica l ex-pe r i m en t s . us i ng Mr . B oy l e ' s Imp rov ed Eng i ne , Ju l y t 663 , " B M Sloane MS 1326,f f. 46- -4 8. I- Ie was one of the f i r s t sc ient i s t s to g ive indep ende nt conf i rm at ion o fBOYLE'S exper iments on the a i r pump.

112 HEN RY POWER, t663, op. ci t . , pp. 121--122.




a fe w e x p e r i m e n t s o n s ip h o n s , w e re i n c o m p l e t e i y e x p l a i n e d a n d i n c l u d e d a s

c u r i o s i t i e s .

I n 1 65 3 h e w a s a w a r e o f PA SC A L'S e x p e r i m e n t , w h i c h s u p p o r t e d T O RR IC EL LI 'Sp r e d i c t i o n t h a t w a t e r s h o u l d r is e t o 33 f e et w h e n s u p p o r t e d b y t h e w e i g h t o f

t h e a t m o s p h e r e . ~ te h a d , h o w e v e r , b e e n u n a b l e t o c o n s t r u c t a n a p p a r a t u s to

c o n f i r m t h i s e x p e r i m e n t . T h e y n o w a t t e m p t e d i t a g a{ n a t T o w n l e y H a l l , l~a a n d

t h e i r a c c o u n t i s i n t e r e s t i n g i n i l l u s t r a t i n g t h e t e c h n i c a l i m p e r f e c t i o n s o f t h e i r

m e t h o d s . I t w a s n o t p o s s i b l e t o c o n s t r u c t t h e a p p a r a t u s i n g l a s s ; t h e r e f o r e , t in

t u b e s w e r e c o n s t r u c t e d o u t o f s h e e t s o f t i n ; t h e s e w e r e f a s t e n e d t o g e t h e r b y

p e w t e r s o l d e r t o f o r m a t u b e 33 f e et lo n g . T h e o n l y p a r t o f t h e a p p a r a t u s m a d e

o f g l a ss w a s t h e e n d s e c t io n . T h i s t u b e w a s e r e c t e d a g a i n s t t h e c o r n e r t f i r r e t o f

T o w n e t e y H a l l , a n d i t w a s f il l e d f r o m i t s u p p e r e n d . W h e n t h e t u b e w a s f u ll

o f w a t e r t h e t o p w a s s e a l ed , a n d t h e b o t t o m w a s i m m e r s e d i n a c i s t e r n o f w a t e r .T h e w a t e r f e ll , i t w a s g u e ss e d , t o 3 2 f e e t, b u t i t h a d u n f o r t u n a t e l y f a l le n b e l o w

t h e g l a s s t u b e a n d i t c o n t i n u e d t o s u b s i d e , s in c e t h e r e w a s a l e a k a g e a t t h e

j u c t i o n o f t h e g l a s s a n d t i n t u b e s .

P AS CA L'S e x p e r i m e n t w a s s u p p o r t e d b y a n o t h e r e x p e r i e n c e . A n e i g h b o u r , a t

H e a t h H a l l , n e a r W a k e f i e l d , w i s h e d t o r a i s e w a t e r t o a h e i g h t o f 4 8 f e e t, a n d t h e

s c i e n t i s t s d e r i v e d s a t i s f a c t i o n i n t h e f a i lu r e o f t h i s ' e x e r ci s e .

F o r I r e m e m b e r i n m y Lady Bowles her new V~Tater -work a t Heath-Hal l , near

Wake/ield, w h e r e th e W a t e r i s r a is e d a t l e as t t 6 y a r d s h i g h t h e s i m p le w o r k m a nu n d e r t o o k f i rs t to d o i t b y a s i n g le P u m p ; b u t s e e in g h is e n d e a v o u r s w e r e f r u s t r a t e d ,

he was fo rced to cu t h i s Cy l inde r i n to two Pu mps , and to r a i s e i t , f i r st , e igh t ya rdsi n t o a h e a d - c i s t e rn , a n d t h e n b y a n o t h e r P u m p t o ra i s e i t o u t o f t h a t o t h e r , e i g h t

ya rd s , i n to a c i s t e rn abo ve} 1~

O n 2 7 t h A p r i l , t6 6 t t h e y r e t u r n e d t o th e i r e x a m i n a t i o n o f t h e e l a s t i c i ty o f

a ir , a d o p t i n g t h e a p p a r a t u s w h i c h h a d b e e n u s e d i n t h e i r f ir s t q u a n t i t a t i v e s t u d i e s

i n t 6 5 3 . E q u a l v o l u m e s of a i r a n d m e r c u r y w e r e p l a c e d i n a T o r r i c e l l i a n t u b e

a n d u p o n i n v e r s i o n i n t o a, d i s h o f m e r c u r y , t h e e x p a n s i o n o f t h e i n c l u d e d a i r

w a s m e a s u r e d . T h e n e w f e a t u r e o f t h i s e x p e r i m e n t w a s , t h a t t h e e x p a n s i o n o f

t h e a i r w a s m e a s u r e d a t d i f f e r e n t a l t i t u d e s on P e n d l e H i l l , i - L a n c a s h i r e ,

w h i c h w a s c o n v e n i e n t l y n e a r T o w n e l e y . 11~

A t t h e t o p o f t h e s a i d H i ll , w e p u t i n t o t h e s a m e T u b e 4 2 in c he d lo n g ( w h i ch

was d iv ided in to 102 . equa l d iv i s ions o f spaces ) a s mu ch Qu icks i l ve r , a s be ing s top ' da n d i n v e r t e d , t h e A y r r e m a i n i n g a t t h e t o p o f t h e T u b e , f i l l ' d 5 0/1 5, o r t h e r e a b o u t ,o f t h e f o r e m e n t i o n e d d i v is i on s , a n d t h e q u i c k s il v e r , ti l e r e m a i n i n g p a r t o f t h e T u b e .

T h e t u b e b e i n g t h u s i m m e r s ' d , a n d t h e f i n g e r w i t h d r a w n , t h e i n t e r n a l A y r d i l a t e d

s o a s to f i ll o f t h e a b o v e m e n t i o n e d p a r t s 8 4/7 5 a n d - t h e r e r e m a i n e d i n th e T u b e aC y l i n d e r of Q u i c k s i l v e r c o n t a i n i n g i n l e n g t h t l / 2 6 i n ch e s. W e t r i e d t h e s a m e E x -

, la Ib id . , pp . 131 - -132 . , BoYLE had desc r ibed th i s exp e r im en t i n 1660 , Works,vo l . 1, pp . 28 - -29 . L ike POWER, the Ro ya l Soc i e ty had . d i f f i cu l ty i n ob t a in ing thea p p a r a t u s f o r t h i s e x p e r i m e n t , a n d t h e f i r s t s u c c e s s f u l p e r f o r m a n c e , r e c o r d e d b y

BIRClL was on t6 th Ju ly , 1663; T . BIRCH, 1756/57 op. c i t . , pp . 7~--80, 86, t03, 255,266, 27t, 273, 279, 286, 259.

n4 H~SNRY POWE R, t663, op . c i t . , pp . t3 1- - t 32 . - - GALILEO, 1638; op . e f t .,p p . t 6 - - - t 7 .

i1~ HENRY POWER, 1663, op . c i t . , p . t27 . T he a l t i tud es of the s ta t ion s m en t io ne d

by Pow er were : -Pend le New C hurch - - 850 I t . ; Ba r low (Ba r l ey ) - - 750 f t . ; Pend leHi l l sum mi t o r Beacon , 1,831 f t.

Arch. Hist. Exact Sci., Vol. 2 32



474 C. WEBsTE~:

p e r i m e n t a t t h e b o t t o m o f t h e s a i d H i ll , t h e T u b e s b e i n g fi l l' d , a s a b o ve , a n d t h eA yr 50/15 . d i la t ed to 83/8 . and the Cyl inder was in h e ig ht 11/78 inches . 116

T h e e l a s t i c i t y o f t h e a i r h a d t h u s decreased a s P e n d l e H i l l w a s d e s c e n d e d .

T h i s o b s e r v a t i o n w a s c o r r e l a t e d t o a n o t h e r e x p e r i m e n t in w h i ch t h e " e x t e n d e d "

! A a i r p r e s s u r e w a s f o u n d t o i nc r eas e d u r i n g

~:]: Tab " 5 " & e d e s c e n t i n h ei g h t. A t P e n d l e N e w

" C h u r c h , t h e l e v e l o f m e r c u r y i n t h e

T o r r i c e l l i a n t u b e w a s 28.4, w h i l e a t t h e

s u m m i t o f t h e h i l l i t w a s 2 7 .4 i n c h es .

T h i s r e s u l t w a s c o n s o n a n t w i t h P O WE R 'S

c - f ' t ' o ' z " f o r m e r e x p e r i m e n t o n H a l i f a x H il l,

-~ E w h e r e t h e f a l l w a s l e s s t h a n a n i n c h ,

t h i s "h ill b e i n g c o n s i d e r a b l y l o w e r t h a nP e n d l e H i l l .

I_9 T h e e x p e r i m e n t w a s n o w r e p e a t e d

- u s i n g a t u b e o f 2 6 i n c h e s , w h i c h w a s

4 n d i v i d e d i n t o 31 d i v i s io n s . A t t h e a p e x

t = I s o f t h e h i l l 9 d iv i s io ns o f a i r we re i n -

e l u d e d , a b o v e t h e m e r c u r y . U p o n i n v er -

s i o n i n t o t h e r e s i d u a l m e r c u r y , t h e a i r

e x p a n d e d t o o c c u p y t 7 .8 d i v i s io n s a n d

i t h e m e r c u r y s h o o d a t t 3 . 8 6 i n c h e s . T h ei; ! t u b e w a s a g a i n c a r r i e d d o w n t h e h il t.

i i W e b r o u g h t t h i s T u b e , w i t tI t h e s a m e

i i Mo un ta i n Ay r i n i t, by t he he lp o f a l ong

i i Tub e o f wood , hav in g a d i sh f a s tned to t heopen end o f i t , and bo th fu l l o f Qu icks i l ve r ,

i n to w h ich we p u t ou r Tube ; AB , (which- i n s t r u m e n t y o u h a v e h e r e r e p r e s e n te d )

B a n d a t t h e b o t t o m o f t h e H i l l t h e Q u i c k -

i s i lve r: r o se up un to t he ma rk r a, und e r t he

t 7. d iv i s ion . So tha t t he A yr d i l a t ed , f i l l ' d

of the equal pa r t s 17~ 35, an d the Qu ick-

s i lver in B was in he ig ht i4 /41 , inches , n~Fig. 5. H. POWER, Experimental Philosophy,London, t663;Endplate,Tab. f.TheapparatusforcarryingtheTorriceUian T h e y h a d e n s u r e d t h a t th e s a m etube up Pendle Hil l . Air occupied t he space AE before ex-pansion. This coincidedwith the 9 unit mark. Theairex- sa m pl e of "M o un ta in A y r" wa s m ea s-partded to eith er 17.35 (m) or 17.8 (l). It is obvious t hat u r e d a t t h e t w o a l ti t u d e s . T h e y n o wPOWER'S diag ram is ambiguou s; the t9 ma rk is in the

wron~ pos i t ion and the mean in g o f the va r ious he igh t exchanged h a t a i r f o r " V a l l e y A y r " a n dlevels is not explained

r e p e a t e d t h e e x p e r i m e n t a t t h e l o w e r

a l t i t u d e . A s l i g h t d i f f e r e n c e i n t h e r e s u l t w a s f o u n d ; n i n e u n i t s o f a i r e x p a n d e d

t o 1 7 . 5 8 u n i t s , a n d t h e m e r c u r y s t o o d a t t 4 . 2 0 . 1 1 s

T h e r e s u l t s w e r e n o w p r e s e n t e d i n t a b u l a r f o rm , i n w h ic h t h e m e r c u r y h e i g h t s

w e r e g i v e n i n i n c h e s a n d t h e a i r v o l u m e s i n t h e p r e v io u s L ,' m e n t i o n e d a r b i t r a r y

u n i t s . S c r u t i n y o f t h e d i a g r a m a n d t i le t a b l e w h i c h a c ~ :. om p an ie d t h i s e x p e r i m e n t

116 Ib id . , p . t27; t i le app ar a t us i s shown in Fig ure 5 .

117 Ib id ., p. 128.l~s Ibi d. , p. 128. In POWER'S T able o f res ults o n p. 129, the f inal m er cu ry leve l

was g iven as 14 .02 uni t s ; see Fig ure 6 .



]3oyle 's Law and the Ela s t ic i ty 'of Air 475

shows the m to con ta in num erou s m inor e r ro r s , wh ich a re typ ic a l o f POWER'S

w o r k . T h d l a c k o f a t t e n t i o n t o d e t a il s o f p r e s e n t a t i o n , d i a g r a m s a n d t a b u l a t e d

numer ical resu l ts , contras t lOOWER'S Experimental Philosophy with HOOKE'SMicrographia, whic h was also publi she d by MARTIN an d ALLESTREE, only a

sho r t t ime a f te r POWER'S book . Indeed the p la tes fo r the two .works were be ing

e x e c u t e d a t t h e s a m e t im e in t 6 6 3 . n "

I n th e l o n g T u b e .

~l t the top o f the Hill. { aCt tb , bottoraof it at Barlow,

A g ..... "5'o115 I " - 5o[~; ~) Eq aa lp ar ts

A D : S 4 1 7 5 - ' - 1 1 3 18 i~ o f S p a c e s ,B D : - - l x l a 6 I~ - -xx[78 ) I n c l a e s .

In the leffer Tube.

aCt the top 1At B a r l o w with t ,'lt B a r l o w roitb

~t be Hill. i ~12(r. " iVall,y.aC,r.

A E , - : 9 ~ 9 i 9

A D "XTf 8 i - x7I'~ fi '-- --- -. 17Iy$B D - - - ~318a I - g÷13~ !~ - t41o2

Fig~ 6. H. POWER, ExperimenCal Philfsophy, London, t663; Table from page 129. This is POW~R'S only att em pt at atabular presentation of his results. I t has certain ambiguities. In the uppe r part of the Table the bracket on the righthand side should upply to the first two lines only. The unit s are no t indica ted at all in the lower half of the Table, and

14.02 should be 14.20

The a ccoun t was te rm ina ted wi th a sho r t cons ic te ra tion o f the theo re t ic a l

imp l ica t ions o f these r es u l t s ) ~° Th is a l so w as def ic ien t in c la r i ty o f exp ress ion .

The he igh t o f the m erc u ry in the Tor r ice l l ian tube was ca l led the MercurialStandard, and the d i f f e rence be tw een th i s a nd t he f ina l l eve l o f me rcu ry in the

e x p e r i m e n t M tu b e s ( th e Mercury), was ca l led the Mercurial Complement. E a c h

of these va lues were p resen ted in inches, and the Mercu r ia l S ta nda rd r ep resen t

th e p r e s s u r e o f t h e a tm o s p h e r e , w h e r e a s t h e M e r c u ri a l Co m p le m e n t r e p r e s e n t e d

th e s t r e n g th o f t h e S p r in g o r E l a t e r y o f t h e a i r e n c lo s e d i n t h e e x p e r im e n ta l

tubes .

The . o r ig ina l vo lum e o f a ir enc losed in the tu be a t a tm osphe r ic p ressu re w as

th e Ayr," t h i s e x p a n d e d , a n d t h e n e w v o lu m e w a s The Ayr Dilated. The d i f f erence

b e tw e e n th e s e tw o v a lu e s w a s t h e A yr's Dilation. T h e s e w e r e m e a s u r e d i n e i t h e r

o f tw o d i f f e r e n t a r b i t r a r y u n i t s . TM].

110 L e t t e r s f r o m M A R T Y N a n d A L L E S ~ R Y t o p O W E R , A u g u s t a n d S e p t e m b e r , 1 6 6 3 ,

B M Sloane M S 1 3 2 6 , H. 3 9 - - 4 0 .

12o H E N R Y P O W E R , 1 6 6 3 , o p . c ir . , p p . 1 2 9 - - - t 3 0 . I h a v e g i v e n a p r e l i m i n a r y a n a l y s i s

o f P O W E R ' S r e s u l t s i n a l l e a r l i e r a r t i c l e ; - - s e e f o o t n o t e t t t .

X~l POWER'S original Tab le of results is given in Figure 6 ;, m y amplif ie d an dcorrected vers io n of h is resu l ts is g iven as Ta ble 2 .

3 2 *



476 C: ~VEBSTER

Volume of theo n r , l r ~ A ~ i r

Air Pressure

Table 2. Th e ex Oressures

Altitude (ft.)

(0.41 inch units)I n RA i n c h ~ n ~ t ~

(inches)

~ansions o~ air at di//erent

Long tube

Volume of ex-panded ai r

Reduced mer-cury pressure

800 I 1,800 [

50.15 ~ 50. i5

28.4 27.4

SO0

O

, 28 .4

(0.41 inch units )[ 83~ -8. I(0.84 inc h units) t 7.5( i n c h e s ) 1 1 1 . 7 8 1 1 . 2 6 1 4 . 2

(1) Len gths ind icated in POWER'S te xt diagrams, and Diag ram 1.

(2) The term used by POWER to designate each vo lume.

Short tube(I )

i sooi, , ,oo

28.49 27.49 AEAEBI

17 .3517 .8 AE14.31 13 .86 1 B~]

(2)

~The Ayr

MercurialStandard

The AyrDilatedTheMercury

They now concluded :

So that here is now four Proportionals, and by any three given, you may strikeout the fourth, by C onversion. Transposit ion, a nd D ivision of them. So tha t bythese Analogies you may prognosticate the effects, which follow in all MercurialExperiments, and predemonstrate them, by calculation, before the senses give anExperim ental eviction thereof.12~

Unfor tuna te ly , the reader was l e f t to guess the iden t i ty o f the " four Propor-

t ionals" . However , i t i s poss ible to assess them from the previous paragraphs .

I t i s c l ear tha t th ey were compar ing m ercury va lues• wi th a i r vo lumes . In the

accoun t gave th ree m ercury var iab les - - tke Mercury , Mercur ia l S tandard an d

Mercurial Complement , a nd th ree a i r vo lume var iab les - - Th e A yr , A yr Di la ted

an d Ayr ' s Di la t ion . Two pair s out of these two sets of three mu st be chbsen.

Since i t i s improbable that the above general isat ion would have been made

wi thou t hav ing per fo rmed e lementary ca lcu la t ions wi th the f igures f rom these

experiments , four of the above variables would be chosen which would , enable

the men t ioned "p rognos t i ca t ion" . The i r hypo thes i s would work i f the Mercur ia l

S tand ard an d Mercuria l Complement were compared wi th the A yr and the Ay r

Dilated . The M e r c u r y can be el im inated, s ince i t a lone of the three f igures i s

not a me asure of extern al pressure, nei th er does it a l low predic t ion of the resul ts

o f o ther exper imen ts . The A yr Dilated i s not used s ince i t i s obtained s imply

by sub t rac t ion f rom the two bas ic measurements o f a i r vo lume.

'Thus i f Mercurial s tan dar d = 'P z,

Mercurial compleme nt = P2.

Ayr = v l .

A3~r D ila ted = v2.

The equa t ion P l V l = p ~ % enables the calculat ion of the resul ts of s imi lar experi -

me nts in which one of the values i s unkno wn. I t assumes the inverse proport io-

123 HENRY POWER, 1663, op. cir., p. 130; "e vict ion" is adde d from t he errata.



B o y l e ' s L a w a n d t h e E l a s t i c i t y o f A i r 477

n a l i t y b e t w e e n t h e v o l u m e a n d p r e ss u r e o f a ir , a n d a n y o t h e r a s s u m p t i 0 Ii w o u l d

p r e v e n t t h e p r e d i c t i o n o f t h e r e s u l ts o f f u t u r e e x p e r i m e n t s . I~3

A l t h o u g h P O W ER p r e s e n t e d t h e e x p e r i m e n t a l r e su l ts a n d h y p o t h e s i s i n t h es i m p l e s t f o r m , i t is o b v i o u s t h a t t h i s j o i n t i n v e s t i g a t i o n h a d a c h i e v e d c o n s M e r a b i y

g r e a t e r u n d e r s t a n d i n g o f t h e e l a s t i c i t y o f a ir , t h a n i n th e e x p e r i m e n t s o f t 6 5 3 .

T h e m o s t i m p o r t a n t a d v a n c e s w e r e t h a t t h e h y p o t h e s i s w a s n o l o n g er t h e r e su l t

o f a c o m p a r i s o n b e t w e e n t h e v o l u m e o / a i r a n d t h e he i gh t o~ me r c ur y i n t h e s a m e

t u b e , b u t b e t w e e n t h e v o l u m e o / a i r a n d a m e a s u r e o f i t ' s e las t ic i ty , d e t e r m i n e d

b y t h e c o m p a r i s o n o f t h e a t m o s p h e r i c p r e s s u re a n d t h e h e i g h t o f m e r c u r y i h t h e

e x p e r i m e n t a l t u b e .

T h i s m e t h o d h a d t h e i n it ia l a d v a n t a g e o v e r B O YL E 'S , t h a t t h e v o l u m e o f

a i r w a s m e a s u r e d d i r e c t ly , w h e r e a s i n B O Y L E'S e x p e r i m e n t i t w a s c a l c u l a t e d .

B O Y LE h a d m e a s u r e d t h e p r e s s u r e o f t h e a i r d i r e c t ly , w h e r e a s i n t h e n o r t h e r ne x p e r i m e n t s i t w a s c a lc u l a t e d . T h i s w a s h o w e v e r n o t a s l ia b l e to e r r o r as th e

c a l c u l a t i o n o f t h e v o l u m e i n B O Y L E 'S e x p e r i m e n t .

P O W E R a n d T OW N EL EY h a d b e e n f a m i l i a r w i t h t h e c o n c e p t o f t h e r e d u c t i o n

o f a t m o s p h e r i c p r e ss u r e w i t h a l t i t u d e f o r m a n y y e a r s ; w h e n t h e y o b s e r v e d t h a t

t h e s p r i n g o f ai r w a s i n c r e a s e d b y a n i n c r e a s e i n a lt i t u d e , i t is p r o b a b l e t h a t t h e y

i m m e d i a t e l y a s s o c ia t e d i t w i t h t h e r e d u c t i o n i n a tm o s p h e r i c p r e ss u re . T h u s a

f e w tr i al s w e r e s u f f i c ie n t t o v e r i f y t h i s a n d g i v e t h e m t h e i n t u i t i v e r e a l is a t i o n

o f t h e r e c i p r o c a l r e la t i o n s h i p b e t w e e n t h e p r e s s u r e a n d v o l u m e o f a ir , a l t h o u g h

t h e y d i d n o t v e r i f y th i s o v e r a w i d e r a n g e o f p r e ss u r e s, o r e x p l o re i ts t h e o r e t i c a l

s i g n i f i c a n c e .

H o w e v e r , i n 1 6 6 2 t h e y p e r f o r m e d a s e ri e s o f e x p e r i m e n t s i n co a l m i n e s , a n d

t h e y c a r r i e d a w e a t h e r g l a ss d o w n t h e m i n e a n d n o t e d t h a t t h e w a t e r i n th e

a p p a r a t u s r o s e 3 i n c h e s d u r i n g t h e d e s c e n t. I n t h e s e c o n d t r i a l o f t h i s e x p e r i m e n t ,

P O W E R n o t e d :

N o w w e o b s e r v ' d t h a t i n c a r r y i n g i d o w n o f t h e s a id G l as s in a S c o o p f r o m t h et o p t o t h e m i d d l e o f t h e P i t , t h e r e t h e w a t e r d i d n o t r i se s o m u c h a s i t d id f r o m t h em i d d l e t o t h e b o t t o m , b y h a l f a n i n c h ; s o t h a t i t s e e m s th e r is e o f t h e w a t e r w a sn o * p r o p o r t i o n a l t o t h e G l a s se s d e s c e n t i n t h e P i t . TM

I t w o u l d b e i n t e r e s t i n g t o k n o w i f P O W E R r e a li s ed t h e s i g n if i c an c e o f t h i s

o b s e r v a t i o n i n re l a t i o n t o h i s f o r m e r r u le o f p r o p o r t i o n a l i t y f o r c a l c u l a t i n g t h eh e i g h t s o f m o u n t a i n s , o r to h i s h y p o t h e s i s f o r c a l c u l a t i n g t h e v o l u m e o f a i r a t

i n c r e a s e d p r e s s u r e s .

123 T h e a p p l i c a t i o n o f th i s h y p o t h e s i s m a y b e i l l u s t r a t e d b y a n e x a m p l e t a k e nf r o m o n e o f t h e e x p e r i m e n t s d e s c ri b e d i n E x p e r i m e n t a l P h i l o s o p h y . 5 0 . t 5 t r a i t s o fa i r (v l ) w e r e e n c l o s e d i n a t u b e a t a t m o s p h e r i c p r e s s u r e , w h i c h w a s 2 7 .4 i n c h e s ( Pl) ;t h e h y p o t h e s i s c a n b e u s e d t o p r e d i c t t h e v o l u m e ( v 2 ) a t t h e r e d u c e d p r e s s u r e o f16 . t 4 inche s (p~).

T h e h y p o t h e s i s a s s u m e s t h a t Pl v~= P2 vs.

B y s u b s t i t u t i o n 2 7 . 4 x 5 0 . 15 = ( 2 7 . 4 - - 1 i . 26 ) × v 2

9 0 - v 2 .T h e r e f o r e t h e h y p o t h e s l s p r e d i c t s t h a t t h e a i r w o u l d e x p a n d f r o m 5 0 .1 5 u n i t s t o9 0 u n i t s , w h e r e a s i n t h e e x p e r i m e n t t h i s v o l u t g e e~ x pa nd ed t o 8 4 . 7 5 u n i t s . 2 _ I n t h ee x p e r i m e n t : w h e r e 9 t i ni t s w e r e t a k e n a t 2 7 .4 i n c h es a t m o s p h e r i c p r e s s u r e , t h e p r e d i c t e di n c r e a s e i n v o l u m e a t 1 3 .5 4 in c h e s p r e s s u r e w a s l 8 .3 u n i t s, w h e r e a s t h e e x p e r i m e n t a lr e s u l t w a s 1 7 . 8 u n i t s .

1=4 Ib id ., p, 176.



478 C. WEBSTER:

C e r ta i n i m p r o v e m e n t s in t h e t e c h n i q u e o f e x p e r i m e n t a t io n m a y b e n o t e d i n

th e a c c o u n t o f 1 6 6 t, a l t h o u g h ' i t i s i n a d e q u a t e b y m o d e r n s t a n d a r d s . T h e t u b e s

w e r e c a l ib r a t e d , a n d t h e m o s t a c c u r a t e f i g ur e s w e r e g iv e n t o t h e n e a r e s t / / 2 0 th

b f~an . inch. T he leve ls o f m erc u ry r e ached in the e xpe r im en t were no t l i ab le to

f luc tua t io n , wh ich was one o f the def ic ienc ies o f BOYLE'S exper im en t . The in i t ia l

v o lu m e o f a i r i n c lu d e d i n t h e t u b e w a s c o n s t a n t f o r a n y t u b e u s e d, w h e r e a s i n

the 1653 exper i men ts a d i f f e ren t in it ia l vo lum e was u sed fo r each t r ia l . F ina l ly

. t h e e x p e r im e n ta l r e s u l t s w e r e a r r a n g e d i n a T a b le w h ic h a l l o w e d th e r e a d y c o m -

par i son o f the var iab les .

Befo re cons ider ing the d is semin a t ion o f the works o f POWER and TOWNELEY,

i t i s a p p r o p r i a t e t o c o n s id e r b r ie f l y t h e i r g e n e ra l a t t i t u d e t o t h e p l e n i s t - v a c u i s t

con t rover sy . S ince the i r bas ic p resuppos i t ions showed no change , be tween 1653

and 166 t , i t i s poss ib le to cons ider the ev idence f rom bo t h t r ea t i ses toge ther .In add i t ion , i t shou ld be no te d th a t TOWNELEY'S c r i t i c i sm o f HOOKE,w r i t t e n i n

two par t s , in 1665 and t667 , con ta ined an amp l i f ica t ion o f the op in ions s ta ted

in Exper imenta l Phi losophy .

Both POWER and TOWNELEYw e r e c o n c e r n e d t o r e l a t e t h e e x p e r im e n t s o n

a i r p ressu re to the i r genera l ph i lo soph y o f na tu re , as had been the case wi th th e

F r e n c h o b s e r v e r s : H o w e v e r , t h e r e w a s a d i ff e re n c e of e m p h a s i s ; t h e E n g l i s h

wr i te r s gave mos t emphas is to the sp r ing o f a i r and , s ince th i s had l i~ le r e levance

to the vacu is t -p len is t con t rover s y , there was g rea te r sepa ra t ion o f the d iscussion

of the expe r ime n ta l and ph i lo soph ica l p rob lems . BOYLE, even more th an TOWNE-

LEY and POWER,b y 2 p as s e d t h e p h i los o p h ic a l p r o b l e m a n d w a s c o n t e n t w i th

a m e c h a n ic a l r e p et i t i o n o f t h e v a c u i s t a n d p l e n is t a r g u m e n t s , w i th o u t i n d i c a t i n g

his own alig nm ent . 1~5

Nei th er d id BOYLE'S a t t i tud e change in the second ed i t ion o f the N e w E x pe r i -

ments Phys ico-Mechanical . HOBBES accused h im o f adher ing to the vacu is t

p h i lo s o p h y, b u t BO Y LE in d ig n a n t ly a c c u s e d h i s o p p o n e n t o f m i s r e p r e se n t a t i o n .

For nei ther has the society decl ared ei ther for or agains t a vacuum , nor h ave I :nay, I .have not only forborn to profess my self a Vacuist, or a Plenist, but I have illa f it place in rr~, epistle expressly said, th at I rese rve the declaring of my oven opinion

touc hing the ~o'~int to ano the r discourse.TM

O n t h e ~ th e r h a n d , P O W E R a n d T OW NE LE Y w e r e p le n i s ts a n d b o th b a s e d

the i r phys ics on Car tes ian p r inc ip les . Th is i s genera l ly over looked in d i scuss ions

o f the C ar tes ian in f luence in Eng land . Whi le the Car tes ian in f luence on the

phi loso phy of MORE and t he phys ics of BOYLE is well kno wn, POWER an d TOWNE-

LEY h a v e b e e n o v e r lo o k e d , a l t h o u g h th e y p r o v id e o u t s t a n d in g e x a m p le s o f

dev~ ' i0n to Car tes ian phys ica l p r inc ip les among Eng l i sh sc ien t i s t s o f the mid -

s e ~ h te e n th c e n tu r y . ~27

-"i'i2~,I{. BOYLE, t660, op. cit., Works, op. cit., v01. 1, pp. 24-- 25, 37, 48 --49 .

#~,\ ~2~ Ib id ., pp . t2 1- -1 22.• ,27 The i mp ort an ce of POWER and TOWXELEV in the hi sto ry of Carte gianism in/. '~England is overlooked in the two most important articles on this subject. MARJORiE

NICOLSON, Th e Ea rly Stag es of Ca rtesi anis m in, En glan d, Studies in Philology, 1929,26, pp. 356----374. S. P. LAMI~RECrt'r, Th e Role of De scar tes in Se ve nte en th, Ce nt ur yEngland, .Studies in the History o/ Ideas (Columbia University, New York), t935,3. pp. 181--242.



]3oyte 's Law and the Elas t ic i ty of Air 479

TOWNELEY and POWER were a ware tha t there was l i t t l e s upp or t fo r Ar is to t -

e l i an p h y s i c s a m o n g th e i r c o n t e m p o r a r i e s , a n d b o th r e a l is e d t h a t t h e v a c u i s t

ph i lo soph y was in the ascen dency in Eng land . TOWNELEY'began h is "Pre l im inar i eD i s c o u r s e " w i th t h e s t a t e m e n t t h a t h e w o u ld b a s e h i s w o r k o n t h e p r in c ip l e s

o f "Mot ion , R es t , f igu re a nd S ize , ye p r inc ip les I th inke on ly to bee ma de use

o f i n y e S o lut i o n o f P h y s i c a l l p r o b l e m e s " , a n d t h a t h e h a d a d o p te d t h e "Ca r t e s i a n

H y p o th e s i s e x c lu s iv e ly t o a n y o th er e . I k n o w th a t t h o u g h I h o p e fo r f a v o u r

e v e n i n t h i s p a r t i c u l a r , f o r b y w h a t I h a v e s e e ne it a p p e a r e s t o m e e , t h a t d e s

Car tes and E p icu re , (o r r a the re Gassendus ) a r e a t ye head o f ye two f ac t ions

which ten d fo r super io r i tee in th i s m en t ion 'd Ph i lo soph ica l l r e fo rm at ion . ''1~8

H e w e n t o n t o j u s t i f y Ca r t e s i a n p r in cip le s , a n d d e v o te d ' t h e m a jo r i t y o f hi s

d iscuss ion to the den ia l o f va cu um and ju s t i f ica t ion o f ae ther . 129

POWER too , in the Prefa ce to Experimental. PhilosOphy, a n n o u n c e d t h e p r in -c ipl e s o f t h e " e v e r - t o - b e - a d m i r e d D e s - Ca r t e s " w h ic h h e i n t e n d e d t o f o l lo w in

his work .

He r ea l i sed tha t the Tor r ice l l ian expe r im en t c r ea t ed d i f ficu l t ies fo r h i s Car -

t e s i a n l~r in cipl es , a n d t h a t F r e n c h o b s e r v e r s f a v o u r e d t h e i d e a o f v a c u u m . H e

th e r e f o r e p r o p o s e d t h a t :

whereas they Will have Rarefact io n and Condensat ion to be per forme d withoutan y increase or toss of quanti ty (which can never be conceived) .we adm it of an aether ialsubstance of Matter in tromit ted and excluded, the Bodies so changed as we former lyex pli cat ed. 130

At the sa me t i me POWER rea l i sed tha t the sp r ing o f a i r cou ld be exp la inedby the va cu is t ' s p r inc ip les as wel l as the p len is t , bu t he p re fe r r ed to r e ta in , the

concep t o f ae ther . TM

H is r e a s o n s f or d e n y in g v a c u u m w e r e l a r g e ly Ca r t e s i a n ; t h e c o n c e p t w a s

"n o n - p h i lo s o p h ic a l " , "v e r y r i d i c ulo u s ; " a ll v o lu m e s h a v in g e x t e n s io n m u s t c o n -

t a in m a t t e r , s in c e e x t e n s io n w a s t h e d e s ig n a t ion o f m a t t e r .

I n a d d i t i o n h e a d o p te d t h e A r i s to t e l i a n o p in io n t h a t t h e r e c o u ld b e n o m o t io n

in a v a c u u m ; s in c e th e s p a c e a b o v e t h e m e r c u r y i n t h e T o r r i ce l l i a n t u b e

t r a n s m i t t e d l i g h t a n d m a g n e t i s m , a n d s in c e t h e s e w e r e s u b s t a n c e s , t h is s p a c e

:m u s t a l s o c o n t a in a m e d iu m . H i s s t a t e m e n t o f t h i s p r in c ip le i l l u s tr a t e s t h e

p e r s i s t a n c e o f t h e A r i s t 0 t e l i a n n o t io n s o f s u b s t a n c e a n d q u a l i t y , e v e n a m o n gt h e m e c h a n i c a l p h i l o s o p h e r s . . .

Again we have the sensib le ev ict ion of our own eyes to confute th is Supposi t ionalVacuity, for we see the whole space to be Luminous (as by Obser.) N o w L ig h t m u s teither be a Substanc e, or else how should it subsist ( if a bare Quality) in a Vac uity@here the re is not hin g to su pp ort it ?x32

I X . P o w e r a n d T o w n e l e y : T h e i r R e l a t i o n s h i p w i t h B o y l e a n d t h e R o y a l S o c ie t y

Th e expe r ime n ts o f POWER and TOWNELE¥ inc luded va lua b le a dvan ces on

the s tudy o f the e las t ic i ty o f a i r , bu t they were no t pub l i shed un t i l l a te in 1663 .

x~8 RICHARDTOWNELEY, "'A Preliminarie discourse by way of Preface, 10th April,1667," f f . [3 , - -4] . This is the in troductory chapter to the work already mentioned: - -~ee footno te 110.

129 Ibi d., ff. [ 13- -27 ].x3° HE NRY ~OWER , 1663, op. cir., p. 132.181 Ibid., p. 133.

ls~ Ibid., p. 95.



480 C. WEBSTER :

I t w o u l d C o n s i d e r a b l y r e d u c e t h e i r s i g n i f i ca n c e i n t h e h . is to r y a n d s c i en c e i f t h e y

w e r e n o t c i r c u l a t e d t o a w i d e r a u d i e n c e b e f o r e t h i s d a t e , s i nc e th e s e c o n d e d i t i o n

o f t h eNdw Experiments Physido-Mechanical

a p p e a r e d i n m i d - t 6 62 . I t i s i m p o r t a n t

t o a s se ss th e e x t e n t t h a t P O W E R'S m a n u s c r i p t s w e r e c i r c u l a t e d a n d i n t e g r a t e d

i n t o t h e f a b r ic o f c o n t e m p o r a r y k n o w l e d g e , f o r t h e s i g n i f ic a n c e o f a n e x p e r i m e n t a l

a d v a n c e l i e s n o t 0 n l y i n i t s r e c o r d i n g , b u t a l so o n t h e e x t e n t i t is p u b l i c i se d .

F o r t u n a t e l y , t h e r e i s g o o d e v i d e n c e a b o u t t h e a c t i v i t i e s o f P O W ER a n d

T OW NE LE Y b e t w e e n t 6 6 t a n d t 6 63 f r o m P O W ER 'S c o r r e s p o n d e n c e , w h i c h i s

p r e s e r v e d i n t h e S l o a n e C o l l e c t io n o f t h e B r i t i s h M u s e u m . H i s l e t t e r s s h o w t h a t

t h e i r e x p e r i m e n t s o n a i r p re s s u r e w e re c i r c u l a te d a m o n g s t t h e m e m b e r s o f t h e

R o y a l S o c i e t y , a n d w e r e o f p a r t i c u l a r i n t e r e s t t o R OB ER T BO Y LE .

P OW EI~ b e c a m e i n t e r e s t e d i n t h e a c t i v i t i e s o f t h e R o y a l S o c i e t y a t a n e a r l y

s t a g e , h i s c o n t a c t w i t h t h i s g r o u p a l l o w i n g t h e m t o b e n e f i t f r o m t h e r e c o r d s

o f h is r e s e a r c h e s , w h i le h e i n t u r n w a s s t i m u l a t e d t o p u r s u e n e w i n v e s t i g a t i o n s .

H e f i r s t m e n t i o n e d t h e S o c i e t y i n a i e t t e r t o h is f ri e n d , R E UB E N RO BIN SO N,

o f M a l d o n , E s s e x , o n 3 0 A p r i l , 1 6 6 t, a n d i n t h e s a m e l e t t e r h e r e f e r r e d t o h i s

r e c e n t e x p e r i m e n t s o n a i r p r es s u re .

I h a v e h e r e o n l y s e n t y o u 2 o r 3 o f t h o s e o b s e r v a t i o n s I m a d e i n i t, B e s i d e s th i sw e e tr i e d th e P a s c a l i a n E x p e r i m e n t o f th e d e s c e n t o f W a t e r i n a T i n - T u b e a b o v e

3 2 f o o t H i g h : w h i c h w e e f o u n d t o b e e x a c t l y t r u e a n d p r o p o r t i o n a l l to t h e m e r c u r i a l

c y l i n d e r in w e i g h t - - N a y b e fo r e w ee d i s s o l v e d o u y s o c y e t y w e e a l l m a r c h e d t o t h e

t o p p o f P e n d l e H i II , O n e o f t h e 3 f a m o u s H i l ls i n E n g l a n d f o r A l t i tu d e , a n d t h e r e

w e e t r y e d t h e T o r r i ce l l ia n e x p e r i m e n t o f th e d e s c e n t o f m e r c u r y w h i c h w a s n e e rt h e r e a b u n d a n t l y l o w e r t h e n a t t h e b o t t o m o f t h e s a m e H i l t b e s i d e E sic.] B e s i d e ,w e e t r y ' d t h e d i f f e r e n c e o f m o u n t a i n - A i r e a n d V a l l e y - A i r e c o u n t e r c h a n i n g [sic.7 t h e i r

p l ac e s , c a r r y i n g t h e o n e u p p a n d t h e o t h e r d o w n f r o m t h e t o p p e o5 t h e H i l l t o t h eb o t t o m i n T u b e s c l o s e l y l u t e d , t o t r y t h e d i f f er e n c e o f t h e , e l a s t i c i t y ; o f t h e s e e x p e r i -

m e n t s I w i ll s e n d y o u a T r a n s c r i p t o f t h e c h i e f e e r e l o n g : I h e a r e m u c h o f t h e C o l le g e

f o r e x p e r i m e n t a l le a r n i n g y o u w r i t e o f: is t h e r e n e v e r a m e m b e r o f i t th a t y o u . o r

I k n o w t h a t I m i g h t h a v e C o r r e s p o n d e n c e w i t h , ~ i t m i g h t , I p e r c h a n c e d o u s b o t h

a e 0 u r t e s y , la ~

I t w a s a b o u t t h e s a m e t i m e t h a t t h e S o c i e t y h e a r d o f P O W E R'S i n t e r e s t in

s c i e n c e a n d W I L LI A M C RO UN E w r o t e h i s f i r s t l e t t e r t o h i m o n J u l y 2 0 t h t 6 6 t' .! a 4

I t c o n t a i n e d a r e q u e s t f o r P O W ER t o s e n d r e c o r d s - o f h i s i n v e s t i g a t i o n s t o t h e

S o c i e t y ; he c o m p l i e d b y s e n d in g h i s e x p e r i m e n t s o n a i r p r e s su r e a n d m a g n e t i s m ,

o n t 5 h A u g u s t . ~a5

133 H EN RY PO W ER, l e t t e r t o .REU BEN RO BIN SO N , 30 A pr i i~ , 1661 ,%t3M Sloane M S

1 32 6, f f. 1 9 - - 2 0 . T h e f o l l o w i n g r e f e r e n c e s t o P O W E R'S c o r r e s p o n d e n c e w i l l T e f e r t oM S 1 3 2 6 u n l e s s o t h e r w i s e s t a t e d .

134 V~'ILL IAMCROUNE,l e t t e r t o H E N R Y Pow/~R, 2 0 t h J u l y , 1 66 1, f . 2 6 . - - - P O W E R ' S

n a m e w a s i n t r o d u c e d t o t h e R o y a l S o c i e t y b y J O H N T IL LO TS ON t h e f u t u r e A r c h b i s h o po f C a n t e r b u r y , w h o w a s o n e o f P OW E R'S f r ie n d s a n d c o r r e s p o n d e n t s ; h e w a s a n a t i v eo f S o w e r b y n e a r H a l i f a x . T IL LO TS ON r e p o r t e d t o C R O U ~ t h a t P OW E R " h a d m a d ea g r e a t m a n y e x p e r i m e n t s w i t h M r B o y l e 's e n gi n n o t t r y ' d b y h i m , v e r y m a n ym a g n e t i c a l l , a n d s o m e w i t h t h e m e r c u r i a l l c y l i n d e r , " f . 2 6. O n 8 t h M a y t 6 61 , CR OU NE

w a s i n s t r u c t e d b y t h e S o c i e t y t o c o r r e s p o n d w i t h P O W ER . @ . B IR C H , I 7 5 6/ 57 , o p . c i t. ,v o1 . I , p . 2 2 . P O W E R r e p o r t e d - t o T IIvI~ OT SO N t h a t t h e c o r r e s p o ~ l d e n c e w i t h C R O UN Eh a d a l r e a d y b e g u n i n t h e e a r l y s u m m e r o f 1 66 1, f . 2 7.

135 HEN RY POWER, l e t t e r t o CROUNE, I 5 A u g u s t , 1 6 6 t ; f .2 ~ .



B o y l e ' s L a w a n d t h e E l a s t i c i t y o f A i r 4 8 t

CRO UN E r e p l i e d o n 1 4 t h S e p t e m b e r , in a l e t t e r , i n t e r e s t i n g b e c a u s e i t r e f e r r e d

t o B O Y LE 'S p a r t i c u l a r i n t e r e s t i n t h e i r l a t e r e x p e r i m e n t s o n a i r p r e s s u r e a n d h i s

i n t e n t i o n o f r e f e rr i n g to t h e m i n h i s f o r t h c o m i n g r e p l y a g a i n s t L IN U S.I h o l d m y s e l f e v e r y p a r t i c u l a r l y o b l i g ' d t o y o u f o r t h e f a v o u r y o u d i d m e e i n

s e n d i n g h i t h e r y o u r B o o k e o f M e r c u r i a l l E x p e r i m e n t s , a n d I h o p e y o u w i l l n o t t h i n k em e u n k i n d t h a t I h a ve n o t s o o n er r e t u r n ' d y o u b o t h m y o w n e t h a n k e s , a n d t h e

h e a r t y t h a n k e s o f a l l o u r C o m p a n y ( w h ic h I a m c o m m a n d e d b y t h e m t o d oe ) w h e n

I s h a l l i n f o r m e y o u t h a t I c o u l d n o t c o n v e n i e n t l y d o e it b e fo r e , b e c a u se y o u r B o o k e

w a s i ll t h e h a n d o f M r . B o y l e w h o i m p o r t u n a t e l y d e s i r e d i t, f o r a p r e s e n t c o n c e r no f .his own , be in g eng ag ' d w i th one wh o ca l l s h im se lf e F ran s i s e : L inus ( Indeed a

F a t h e r o f t h e S o c i e t y o f J e s :) h e r e i n T ow n , w h o p r e t e n d s a d i ff e r in g H y p o t h e s i s

o f e x p l i c a t e i n g al l t h e m e r c u r i a l l p h e n o m e n a f r o m t h a t o f t h e w e i g h t o f th e A t m o s -

p h e a r . S o m e o f y o u r l a s t e x p e r i m e n t s h a v e d o n n e M r . B o y l e a k i n d n es s e , w h i c h Ia m c e r t a i n e he e w il l m e n t i o n - i n h i s a n s w e r t o L in u s , w h o s e B o o k e I d o u b t n o t b u t

you hav e rece iv ed before th is . 136

T h e l e t t e r c o n t i n u e d w i t h a b ri e f a c c o u n t o f L IN I :S ' h y p o t h e s i s a n d a n a p o l o g y

f o r n o t h a v i n g r e t u r n e d t h e a c c o u n t o f t h e e x p e r i m e n t s on. a i r p r e s s u r e p r e v i o u s l y ,

s in c e t h e y w e r e b e i n g t r a n s c r i b e d b y o n e o f t h e S o c i e ty .

W h e n CRO U•E a c k n o w l e d g e d P O WE R'S r e p l y a g a i n s t L I NU S , i n J a n u a r y 1 66 2,

h e m e n t i o n e d t h a t BO YLE h a d s t i l l n o t c o m p l e t e d h i s r e p l y t o L I N u s , a n d i n t e n d e d

t o us e i n f o r m a t i o n f r o m t h is t r a c t a l s o "

e s p e c i a l l y t h a t o f t h e w e a t h e r g l as s e.

H e a s s u r e d P O W E R t h a t B OY LE i n t e n d e d t o a c k n o w l e d g e t h i s a l s o . !37

B OY LE h a d t h u s i n f o r m e d C R OU NE t h a t h e i n t e n d e d t o u s e i n f o r m a t i o n f r o m

t w o m a n u s c r i p t s , w h i c h t h e l a t t e r h a d p a s s e d o n t o h i m . T h e f i rs t w as t h e e x -

p e r i m e n t s o f t 6 6 0 a n d 1 6 6 t w h i c h w e r e c o n c e r n e d w i t h t h e e l a s t i c i t y of a i r , a n d

w e r e t h e j o i n t i n v e s t i g a t i o n o f P O W E R a n d T O W N E L E Y . T h e s e c o n d w a s H E I ~ R ' Z

P OW E R'S r e p l y t o L I NU S , w h i c h c o n t a i n e d a n e x p e r i m e n t i n w h i c h a w e a t h e r

g l a s s w a s c a r r i e d u p t h e s t e e p h i l l a b o v e h i s h o m e a t E l l a n d , n e a r H a l i f a x .

W e a r e n o w i n a p o s i t i o n t o e l u c i d a t e t h e s c a n t y r e f e r e n c e s b y R OB ER T B OY LE

t o T OW N EL EY 'S w o r k , i n o r d e r t o o b t a i n a n e s t i m a t e o f h i s d e b t t o t h e n o r t h e r n

i n v e s t i g a t o r s .

D i r e c t r e f e r e n c e w a s ~ m a d e t o b o t h P o w E R a n d T OW N EL EY i n t h e s e c o n d

e d i t i o n o f t h e New Experiments Physico-Mechanical w h i c h a p p e a r e d i n t 6 6 2 .

I t w a s o n t h e b a s is o f t h i s w o r k a n d o r a l c o m m u n i c a t i o n s f r o m B OY LE t h a t

t h e p r o p o r t i o n a l i t y b e t w e e n t h e d e n s i t y o f a i r a n d i t s p re s s u r e b e c a m e k n o w n

136 WILLIAM'CROUNE; l e t te r to HENRY POWER, t4 Sept . 1661; f . 25 . - - In a le t t e r

t o ROBII~SO~ (ff. 20 - -21 ) POWER hope d t ha t h i s m anu sc r ip t s wou ld be co mm un ica t ed

to BOYLE, and add ed th a t he was com pos ing a r ep ly t o L INUS ( see foo tno te 111 ).

W h e n t h i s w a s c o m p l e te d , i t w a s s e n t to t h e R o y a l S o c i e t y a n d w a s a c k n o w l e d g e d

by CROUI~E on Ja nu ar y 9 th , 1661/62; I f . 28- -29 .1~7 \¥ILLIAM CROUNE, le t t er to HENRY POWER, 9 Ja nu ar y, t661/62, f . 28. - -

POWER sen t expe r ime n t s on s ipt~ons and cap i l l a r i e s t o t he Soc i e ty i n Fe b ru a ry ,

t661/62 , BM Sloane M S , 1393, f . 166). Thes e were a ckn ow led ged by CROUNE onMarch 1s t 1661 /62, a nd in t he s am e l e t t e r he r epo r t ed t ha t BOYLE 'S r ep ly t o L INUSwas no t y e t pu b l i shed ; f . 30. I t h ad no t app ea r ed by M ay 17 th (f. 31) , and i t wasf ina l ly Sent to POWER on Oc tob er 16th 1662 ( f. 32). POWER wro te a l e t t e r of ackno w-

ledge men t t o BOYLE on 10 Novemb er , 1662, wh ich was enc losed in a fu r the r l e t t e rt o CROUNE on 19 Novem ber , 1662 ; If . 33 - -34 . The re was c onseq uen t ly no d i r ec tco r r e spond ence be tw een POWER and BOYLE .



482 C. WEBSTER:

a s "T o w n e l e y ' s h y p o t h e s i s " % r " T o w n l e y ' s T h e o r y " b y s e v e n t e e n t h c e n t u r y

au tho r s , suc h a s HOOKE an d NEWTON. 1as

A s h a s b e e n p r e v i o u s l y n o t e d , 139 t h e s e c o n d e d i t i o n o f B OY LE 'S w o r k w a s i nt h r e e p a r t s , w h i c h w e r e p r o b a b l y a v a i l a b l e s e p a r a t e l y . T h e e x p e r i m e n t s o f t h e

t 6 6 0 e d i t i o n f o r m e d t h e b u l k o f t h e v o l u m e , a n d t h e r e m a i n d e r c o n s i s te d of a

r e p l y t o I-IO BB ES a n d o n e t o L IN U S . I t w a s i n t h i s l a s t p a r t o f t h e w o r k , w h i c h

w a s w r i t t e n d u r i n g t h e c l o s i n g m o n t h s o f 1 6 6 t , t h a t B O YL E r e t u r n e d t o a n e x-

p e r i m e n t a l i n v e s t i g a t i o n o f t h e e l a s t i c i t y o f a ir . I h a v e i n d i c a t e d t h a t h e h a d

t h e e x p e r i m e n t s o f PO W ER a n d T OW NE LE Y t o a i d h i m ; a s w e l l a s c e r t a i n c o n t r i b u -

t i o n s b y m e m b e r s o f th e R o y a l S o c i e t y , w h i c h w i l l b e r e f e r r e d t o i n t h e f o l l o w i n g

a c c o u n t .

L IN U S h a d p r o p o s e d t h a t tt{ e m e r c u r y i n th e T o r r i c e l l i a n e x p e r i m e n t w a s

s u p p o r t e d b y a r a r e f i e d c o r d o f m e r c u r y o r f u n i c u l u m . B OY LE s a w t h a t P AS CA L'SP u y d e D 6 m e e x p e r i m e n t w a s a n " e x p e r i m e n t u m - c r u c i s " s u p p o r t i n g t h e c o n c ep t

o f t h e w e i g h t o f a i r, s i n c e t h i s h y p o t h e s i s r a t h e r t h a n t h e f u n i c u l u m w o u l d e x p l a i n

t h e m e r c u r y ' s d e s c e n t w i t h i n c r e a s e d a l t i t u d e . 140 B OY LE , l i k e m o s t o t h e r E n g l i s h

o b s e r v er s , h a d t a k e n t h e d e t a n s o f t h i s e x p e r i m e n t f r o m I~ECQUET.

L IN U S h a d n o r e c o u r s e b u t t o d e n y P AS CA L'S e v i d e n c e , a n d B OY LE r e t o r t e d t h a t

t h e t r u t h o f P AS CA L'S e x p e r i m e n t h a d b e e n c o n f i r m e d b y t w o E n g l i s h o b s e r v e r s .

E s p e c i a l l y s i nc e I c a n c o n f ir m t h e s e o b s e r v a t i o n s b y t w o m o r e m a d e o n d i s t a n t .

h i l l s in England. T h e o n e w h i c h I p r o c u r e d f r o m t h a t k n o w n V i r t u o s o M r. J . B a l l,

w h o m I d e s i r e d t o m a k e t h e e x p e r i m e n t a t a m o u n t a i n i n Devonshire , o n t h e s i d e

t h e r e o f ' h e d w e l t ; a n d t h e o t h e r m a d e i n Lancash i re b y t h a t i n g e n io u s g e n t l e m a nM r. Rich . Townley . B o t h w h i c h o b s e r v a t i o n s , s i n c e ! h a v e m e n t i o n e d t h e m a t l a r g e

i n t h e A p p e n d i x t o t h e P h y s i c o - M e c h a n i c a l t r e a t is e , I s h a l l n o t n o w r e p e a t ; c o n -t e n t i n g m y s e l f t o o b s e r v e t o o u r p r e s e n t p u r p o s e, t h a t h o w e v e r t h e p r o p o r t i o n o f

t h e d e s c e n t o f q u i c k s i l v e r m a y v a r y , a c c o r d i n g t o t h e d i f fe r i n g c o n s i st e n c e a n d o t h e r

a c c i d e n t s o f t h e n e i g h b o u r i n g a i r , in t h e p a r t i c u l a r p l a c e s a n d t i m e s o f t h e ' e x p e i - i m e n t sb e i n g m a d e , y e t a l l o b s e r v a t i o n s a g r e e in th i s , t h a t n e a r e r t h e t o p o f t h e a t m o s p h e r e

t h e q u i c k s i l v e r f a ll s l o w e r t h a n i t d o e s f u r t h e r f r o m i t . T o t h i s I s h a l l a d d t w o t h i n g s,

t h a t w i l l v e r y m u c h c o n f i r m o u r h y p o t h e s i s . T h e o n e i s, t h a t t h e f r e s h y n a m e d M r .Townley, and divers ingenious persons that assisted at the tr ial , bethought themselves

o[ so mak ing the T orrice l l ian ex per ime nt at the top o[ the hi l l, as to leave a determinate

quanti ty o[ air in the tube, be[ore the mouth o[ i t was opened under the vessel led mercury;

and taking notice how low such a quanti ty o[ that air depressed the mercurial cyl inder,they l ikew ise observed, that at the moun tain 's loot the included air was not able to depressthe quicksi lver so much. W h e n c e w e i n fe r , t h a t t h e c y l i n d e r o f a i r a t t h e t o p o f t h e h i l l

b e i n g s h o r t e r a n d l i g h te r , d i d . n o t s o s t r o n g l y p r e s s a g a i n s t t h e i n c l u d e d a i r , a s d i d t h ea m b i e n t a i r a t t h e b o t t o m o f t h e h i l l, w h e r e t h e a e r ie l c y l i n d e r w a s l o n g e r a n d h e a v i e r, m

T h i s q u o t a t i 9 n . re q u i re s c e r t a i n c l a r i f i c a ti o n . S i n c e BO YL E i n c l u d e d n o f u l l e r

a c c o u n t o f t h e o b s e r v a t i o n s o f B A LL a n d T OW NE LE Y a s a s e p a r a t e a p p e n d i x ,

d i d h e re f e r t o t h e m a t a n o t h e r p o i n t i n h i s w o r k , a n d h a v e t h e i r a c c o u n t s b e e n

p r e s e r v e d ?

138 R. BOYLE, t662, op . c i r . , Works , op. ci t . , vol . 1; p. 102. - - R . HOOKE,Micro-

graphia, Lo ndo n, t665, p . 225. - - Fo r NEWTON'S references to TOWNELEY'S hyp oth es is ,see I. BERNARD COHEN,,N e W t o n, H o o k e a n d B o y l e ' s L a w ; D i s c o v e r e d b y P o w e r

a n d T o w n e l e y , Nature , 1964, 204, pp . 6 t8 - -6 21 .

lg9 See note 87.140 1{. BOYLE, t662 op . c i r . , Works , vo l . 1, p . 97. Th i s acco un t fo rm ed t he f i r s t

p a r t o f C h a p t e r 4 o f P a r t I I o f t h e r e p l y to L IN US .~a~ Ib id . , p . 98 . I have i n se r t ed t he ' i t a l i c s a t t h e e nd o f t he q uo ta t i o n .



Bovle's Law and the Elasticity of Air 483

In the earlier edition of New Experiments Physico-Mechanical, he referred

to BALL'S experiment, which had been pe rformed in the Wes t.o f England . This

account was later given to the Royal Society, and preserved in the RegisterBook.14z

TOWNELEY'S descr iption of this experiment was not alluded to elsewhere in

BOYLE'S work, but exam inati on of the passages which I have Placed in italics

in the above quotati on, m ake it obvious tha t BOYLE was referring to the first

of the manuscripts sent to him by POWER.

The first pa rt of the passage refers to the title of the m anusc ript, 143 which

referred to the experiments performed at Towneley Hill "by the advice and

assistance o~ that Heroick and W or thy Genlleman, Mr. RICHARD TOWNLEY,

ES QR. and those Ing en iou s Gentlemen Mr. JOHN and Mr. CHARLE S TOWNLE Y

and Mr. GE O R G E KEMP. 'u44The sequence of events and results of the experiment are exactly as POWER

described them in his acco unt , which has already been .quoted, 145 BOYLE'S con-

cludfng remarks about the experiment ma ke it probable that he did not under-

stand the significance of the hypothesis which was suggested at the end of the

experiment. This was probably too crypt ic for BOYLE to derive the idea of the

reciprocal proportions between the volume of air and pressure.

Thus, BOYLE received the above m anuscr ipt from CROUNE at the end of

Augus t, 1661, when it prob ably inspired the structure of. the fo urth chapter of

the reply to Lne vs; he quoted from the most significant experiments i n the

manuscript, but misread the title and attributed its ,composition to TOWNELEY,

while there was no internal evidence to suggest that it was actually written

by POWER.14e

We ha ve no fur ther records of experiments on air pressure by TOWNELEY

and POWER, althou gh their 'ac tive research conti nued a fter 1662. POWER'S conta ct •

with the Royal Society gave him the opportunity to prepare his pamphlets for

14~ Register Book of the Royal Society, BM Sloane MS 243, ff. 94--95 ; "Accountof the quicksilver experiment of Mr. Ball." This was an account of experimentsperformed between October 1659 and February t 660, presumably by WILLIAMBALL,

at his estate at Mamhead~, S. Devon. The account was read at the meeting of theRoyal Society in December 166t, "Mr. Balle brought in his account of the quicksilverexperiment at Mainhead [sic.]; which was ordered to be registered." T. BIRCH,1"756/57, op. cir., vol. I, p. 67. BOYLE'S reference was to Mr. J. BALL, bu t BIRCHmentioned only WILLIAM BALL (1627--1690), who was in the original committee,established by the Society, to examine to Torricellian experiment. He was also askedto communicate with POWER, presumably about the Puy de D6me experiment. SeeT. BIRCH, t756/57, op. cir., vol. t, pp. 12, 22, 25, 66--67.

14a The full title of the manuscript is given on p. 472.x44 H. POWER, t663, op. cit., p. 121.145 .See p. 473--475.14~ At the end of Chapter 4 of Part II of the reply to LINuS, BoyLE made direct

reference to POWER'S own reply to LINUS. BOYLE stated that he had casually met"with an experiment lately sent in a letter to a very ingenious acquaintance of hisand mine ~WILLIAMCROUNE~,by a very industrious physician [HENRY POWER."Their names are given in marginal notes. This was POWER'S account of the Puy deD6me experiment which he had verified again on October 15th 1661. This was alsoincluded in Experimental Philosophy; H. POWER, 1663, op. cit., p. 141 ; R. BOYLE,1662, op. cit., Works, vol. 1, pp. 99--100.



484 C. WEBSTER :

p u b l i c a t i o n , b u t a f t e r t h e a p p e a r a n c e o f Experimental Philosophy, t h e r e w a s a

n o t i c e a b l e d i m u n i t i o n i n h i s c o n t r i b u t i o n s t o t h e S o c i e t y . TO W NE LE Y p a s s e d o n

t o a c r i t i c i s m o f HO O KE 'S w o r k o n c a p i l l a r i t y a n d t h e j u s t i f i c a t i o n o f C a r t e s i a n

m e c h a n i s m .

W h i l e t h e i r f i n a l p u b l i c a t i o n o f t h e i r w o r k o n a i r p r e s s u re w a s d i s a p p o i n t i n g l y

f r a g m e n t a r y a n d a m b i g u o u s , t h e c o m m u n i c a t i o n o f t h e m a n u s c r i p t s t o B OY LE

w a s o f t h e g r e a t e s t s e r vi c e t o h im . T h e y h a d p r o v i d e d a d i r e ct w a y o f m e a s u r i n g

t h e s p r i n g o f a i r a t d i f f e r e n t p r e ss u r e s , a n d f u r t h e r , g i v e n a m e t h o d w h i c h c o u l d

g i v e B OY LE t h e c o m p r e h e n s i v e t a b l e o f r e s u l t s w h i c h . h e h a d s o u g h t i n h i s i n i t i a l '

e x p e r i m e n t s b e f o r e 1 6 6 0 .

X. Boyle ' s Exper iments on the Compress ion and Di lat ion of Air

I n C h a p t e r V . t h e l a s t i n h i s b o o k a g a i n s t L II ~U S, B OY LE r e t u r n e d t o t h e

q u a n t i t a t i v e s t u d y o f th e. s p r i n g o f a i r. T h i s w a s p r o b a b l y p r o m p t e d b y t h e

e x p e r i m e n t s p e r f o r m e d a t t h e w e e k l y R o y a l S o c i e t y m e e t i n g s. A s h a s a l r e a d y

b e e n n o t e d i n J a n u a r y t 6 6 t , a n i n f l u e n t ia l c o m m i t t e e h a d b e e n e s t a b l i s h e d t o

r e p o r t o n t h e T o r r i c e l l i a n e x p e r i m e n t , 147 a n d a t t h e m e e t i n g o n S e p t e m b e r 4 t h

t h e m e m b e r s o f t h e S o c i e t y w e r e i n t r o d u c e d t o t h e i d e a o f c o m p r e s s i n g a i r m

a J s h a p e d t u b e , t h e e x p e r i m e n t b e i n g d e s c r i b e d b y P O W ER 'S c o r r e s p o n d e n t ,

WILLIAM CROUNE.

Mr . Croune was r eques t ed t o p rocu re a syph on o f g l a s s t o be made , w i th t h e end

n ip t up , i n o rde r t o t r y t he comp res s ion o f a i r w i th qu i cks i l ve r , and a l so to t r y anexp e r im en t w i th t he we lgh t o f l i quo r s i n a s i phon . 14s

I n t e r e s t i n s i ph o n s w a s u n i v e r s a l a m o n g s e v e n t e e n t h c e n t u r y s c i en t is t s, a n d

t h i s q u o t a t i o n s h o w s t h a t t h e J - t u b e w a s e v o l v e d b y s i m p l y i n v e r t i n g a n d d o ' s in g

t h e s h o r t a r m o f t h e s i p h o n ; t h i s c o u l d n o w c o n t a i n a v o l u m e O f a i r. w h i c h m i g h t

b e c o m p r e s s e d b y a v o l u m e o f l i q u i d i n t h e l o n g e r a r m B OY LE h i m s e l f h a d p e r -

f o r m e d v a r i o u s e x p e r i m e n t s w i t h s i p h o n s 1~9 a n d h a d u s e d a n i n v e r t e d s i p h o n

f or c o m p a r i n g t h e d e n s i t ie s of w a t e r a n d m e r c u r y , b y m e a s u r i n g t h e h e i g h t s o f

t h e v o l u m e s o f w a t e r a n d m e r c u r y w h i c h b a l a n c e d o n e a n o t h e r . T h u s , i t p r o v i d e d

a m e t h o d f o r m e a s u r i n g t h e volume o/ai r a n d t h e pressure i n a s i n g l e a p p a r a t u s .

a l t h o u g h t o o b t a i n t h e t o t a l p r es s u r e on t h e a i r t h e a t m o s p h e r i c p r e s s u r e w as

r e q u i r e d a l s o. T h e w e a k n e s s o f t h e a p p a r a t u s w a s a t t h e s e a l e d e n d , w h i c h w a s

l i a b l e t o b r e a k u n d e r t h e p r e s s u r e , a s C RO UN E f o u n d a t t h e n e x t m e e t i n g .

M r. C r o u n e p r o d u c e d t w o e x p e r i m e n t s , o n e o f t h e c o m p r e s s i o n o f a ir w i t h q u i c k -s i l ve r i n a c rodked tub e o f g la s s , t he n ip t end o f wh ich b rok e ; . . .

M r . B o y l e g a; ee a n a c c o u n t o f h i s h a v i n g m a d e t h e f o r m e r o f th e s e e x p e r i m e n t sb y c o m p r e s s i n g t w e l v e i n c he s o f a ir t o t h r e e i n ch e s, w i t h a b o u t a h u n d r e d i n c h e s

of qui cks i lve r . 1~°

A l r e a d y BO YL E h a d a n i n t u i t i v e u n d e r s t a n d i n g o f t h e n a t u r e o f t h e r e l a t i o n -

s h i p b e t w e e n t h e e l a s t i c i t y of a i r a n d i t s p r e s s u r e , h e r e a l is e d t h a t a n e x t r e m e l y

14v T. BIRCH, 1756/57, op . cit ., VO1. 1, pp . 8, 10, 12, 16, |t). BOYLE'S ai r p u m pwax~ f i r s t dem ons t r a t ed a t t he mee t ing on tS t h May , 1661 ; Ib id . , p . 23.

14~ Ibid., p. 43.149 It . l~c)vLI;., 1662. p. c ir ., Works, vol. t , pp . 5t 57-1.~o T. BIRCH, 1756/57 op. t i t . , p . 45. Thi s d em on st ra t io n was at the m ee tin g on

11 September, 1961.



Boyte's Law and the Elasticity of Air 485

long arm was required for the mercury, since the spring ol air increased consider-

ably as its volume diminished.

On Sep tember t Sth his investigation progressed further, and he p resentedtile Society with a table of results, showing the relationship between the volume

of air and the height of mercury. This indicated the nature of the spring of air

even more clearly, TM and this Table, which was entered in the

Regi'ster Book on October 2nd, t 66t, had a list of results which ~¢~ ].o • |

was identical to tha t in the Table produced in the second edition v IO.

of the New Experiments in the nex t year. 153 The detailed account A

of this experiment, which was probably the one performed before

the R oya l Society in September t662, formed the first part of

Chapter V, the last chapter of his reply to LINUS.153

The greatest technical difficulty in the experiment was theproduction of tubes of even bore and a long enough arm. Many

tubes were broken in the trials. 154 In the published experiment the

short arm was 42 inches long and the long one about 120 inches.

As in the experiments of 1660, he gave full experimental

details, paying particular attention to causes of error, and techni-

.cal difficulties. In particular the grea t length of the mercurial

tube necessitated two persons to perform the experiment, one

slowly pouring mercury in, and the other measuring the volume

of the compres sed air. 155 An improveme nt on the experimen ts

Of POWER and TOWNELEYwas that the volumes o/fir and mercurywere measured in inches, and the smallest units calibrated were

6- inches-~5~ The results were given in bo th inches and ~ inches.

It is interesting that none of the observers used a decimal system

of calibration. The mercury was gradually poured in and its

vertical height was recorded at each reduction of the air's volume C.~Iby 2- an inch, between t2 inc hes and 6 inches; when the volume

of air had been reduced by a half, the measurements were made ~11 |~ ,

at each subsequent } inch of compression.

The observat ion which BOYLE notes with the greatest pleasure

was th at the volume of air was halved when the mercur y stood

at 29 inches in the long arm, tha t is, when the pressure on the

enclosed air was doubled. He now arrived at the following hy po- rig. 7. E. BoY~,thesis. Ne~ Experiments

Physico-Mechani-cal, London, t 662;

Now that this observation does both very well agree and confirm Works, ol.t,End-our hypothesis, will be easily discerned by him that takes notice what plate Fig. 16.

BOYLE'S J-tube

we teach; and Monsieur Pascal and our English friend's experiments apparatusprove, tha t the greater the weight is tha t leans upon the air,'-the

xs~ Ibid., p. 45. D. McKIE has reproduced BOYLE'S Table of results from themanuscript Register Book of the Royal Society; op. cir., see footnote 2.

152 R. BOYLE , 1662, . op. cir., Works, vol. 1, p: 101.

~ss Ibid., pp. 100--102. The title of Chapter 5 was "Two riew Experimelits touchingthe measure of the force of the spring of air compressed and dilated."

~s~ Ibid., p. 101. BOYLE' S J-tube apparatus is shown in Figure 7.~ss Ibid., p. 101.

~ss Ibid., p. t00.



486 C. WEbSTEr:

more forcible is its endeavour of dilatation, and consequently its power of resist-ance (as other springs are stronger when bent by greater weights). For this beingconsidered, it will appear to agree rarely-well with the hypothesis, that as accord-

ing to it the air in that degree of density and correspondent measure of.. esistance,to which the weight of the incumbent atmosphere had brought it, was able tocounterbalance and resist the pressure of a mercurial cylinder of about 29 inches,as we are taught by the Torricellian experiment; so here the same air being broughtto a degree of density about twice as great as that it had before obtains a springtwice as strong as formerly.TM "

BOYLE acknowledged no assistance in evolving this hypothesis, although he

noted th at it was in accord with his "En gl is h friend's experiments". Once the

experiment was devised and the importance of noting the barometric height as

well as the mercur y height was realised, it would have been obvious, even to one

of the slight math ema tica l ability, that "th e resistance to compression had dou-bled w ith the doubling of the pressure", iSs

It should be emphas ised that BOYLE'S Law, as evolved during September

166t, stated t ha t the spring of air (its resistance to compression) is proportio nal to

its density. This particular expression of the law is rarely mentioned by historians

of science.

It is by no means certain tha t he realised at }his time th at this expression im-

plied reciprocal proportion between the external pressure and the "Expansion"

of a volume of air. This expression occu rred on ly in a later place in the chapt er

and in the notes 'appended to the tables of results? 59

He now wished to examine the influence that the expansion of air had on its

pressure, or Spring. For this he used a modified form of the Torricellian apparatus.

The tube was six feet long, and this ~ould be almost completely submerged in a

cylinder of mercury. One inch of air was included in the tube, which was sub-

merged in the mercury, with only the inch of air protruding. The tube was now

raised and the height of mercury recorded for each increase of one inch in the

volume of included air. La t e r in the experiment the mercu ry level was measured

against larger increases in the volume of iar.! 6° As in the former exper iment he

tabulated the results, giving the mercu ry heights against air volumes ?6~ It may seem

strange to the mode rn observer that BOYLE could not reduce these results to anyhypothesis, considering that he had already produced an hypothesis for the

compression of air. The barrier to und ers tan din g'th e application of this hypo-

thesis to the expansion experiment may have been his failure to understand that

the tr ue pressure of the vo lu me of contained air was obtaine d from. the baro-

metric height minus the height of the mer cury in the tube. Thus it was necessary

for BOYLE tO realise that , in the J- tu be exper iment, spring = Barometric height +

mercury height in the long arm, while in the dilatation experiment, spr ing+

mercury height- Barometric height.

ls~ Ibid., p. tOO.

158 Ibid., p. 701.

ls9 In this article it is assumed that the order of experiments described by BOYLEin Chapters 4 and 5 of Part II of the reply to LINUS represents a continuous chrono-logical sequence of composition..

16o Ibid. , .pp. t02--103.161 Ibid., p. 102.



]3oyl e 's L aw and t he E l as t i c i t y o f A i r 487

P e r h a p s i n B OY L E' S m i n d t h e r e s t i ll li n g e r e d t h e s c h o l a s t ic n o t i o n t h a t c o n -

d e n s a t i o n a n d r a r e f a c t i o n w e r e q u a l i t a t i v e l y d i f f e r e n t .

I n t h e p r e v i o u s e x p e r i m e n t t h e t a b l e o f r e s u l ts s h o w e d t h e d e c r e a s e i n t h e a i r ' sv o l u m e w i t h i n c re a s e in th e m e r c u r i a l c o i u m n , e v e n w i t h o u t a d d i t i o n o f t h e b a r o -

m e t r i c h e i g h t to t h e t o t a l p r es s u re s u s t a i n e d b y t h e m e r c u r y : t h e a i r v o l u m e

r e d u c e d f r o m t 2 t o 3 i n c h e s as t h e m e r c u r i a l c o l u m n i n c r e a s e d f r o m 0 t o 88½

inches .

B u t t h e t a b l e o f r e s u l ts f o r th e d i l a t i o n e x p e r i m e n t w a s le ss cl ea r. T h e i m m e d i a t e

s e t o f r e s u l t s g a v e t w o in c r e a s i n g m a g n i t u d e s , f o r a s t h e a i r e x p a n d e d t h e m e r c u r y

c o l u m n i n c r e a s e d i n h e i g h t . T h e p r o p o r t i o n a t e c h a n g e s m i g h t a l s o h a v e b e e n

c o n f u s i n g , s in c e , a s t h e v o l u m e o f a i r in c r e a s e d f r o m t t o t 8 i n c h e s, t h e m e r c u r y

inc reased f rom 0 t o 26 i nches ; whi l e a s t he a i r i nc r eased f rom 8 t o 32 i nches , t he

m e r c u r y o n l y i n c r e a s e d f r o m 2 6 t o 28 ~- i n c he s . D i r e c t c o m p a r i s o n s b e t w e e n t h e s e

r e s u l ts w o u l d t h u s h a v e b e e n f a r m o r e c o n f u s i n g t h a n b e t w e e n t h e d i r e c t r es u l t s

o f t h e p r e v i o u s e x p e r i m e n t . T h e y w o u l d c e r t a i n l y n o t h a v e i n d i c a t e d t h e " d e b il i-

t a t i o n o f t h e f o r c e o f t h e e x p a n d i n g a i r " .

B e f o r e p r e s e n t i n g t h e .t ab le i n it s fi n a l fo r m , s h o w i n g t h e a g r e e m e n t o f t h e

resu l t s w i th h i s own hypo thes i s , BOYL E expres s ed h i s i nde b t ed nes s t o RICHARD

T OW NE L E Y for c l a r i fy ing t he mean ing o fh i s r e su l t s .

. , . I shall readi ly acknowledge, t ha t I had no t reduced the t r ia l s I had. ma dea b o u t t h e m e a s u r in g t h e e x p a n s i o n o f a ir t o a n y c e rt a in h y p o t h e s i s , w h e n t h a t

i ngen ious gen t l eman Mr . Ri chard Tow nl ey was p l eased t o i n fo rm me , t ha t hav ingby t he pe rusa l Of m y ph ys i comechan i ca l expe riment s , been sa t is f ied t h a t t he sp r ingof t he a i r was t he c aus e o f i t, he endeavo ured ( and I w i sh i n such a t t emp t s o the ringenious men would fo l low h is example ) t o supp ly w ha t I had omi t t ed conce rn ingthe re ducin g to a precise es t imate , how mu ch a i r d i la ted i t se l f loses of i t s e last ica lfo rce , accord ing to t he measure o f it s d il a t at i on . He added , t ha t he had begun t oset down what occurred to him to th i s purpose in a ahor t d i scourse , whereof he af ter -wa rds d id me the f a vour t o show m e the beg inn ing , which g ives me a j us t cu r ios i tyto see i t per fec ted. But , because I ne i the r know , nor (by reason of the g reat d i s tancebetwix~ our places of residence) hav e a t pres ent the o pp or t un i ty to inqui re, w heth erhe wi l l th ink f i t to annex his d i scourse to ou r appendix, or to pub l i sh i t by i t se lf ,or a t a l l ; and because he ha th not y et , for au gh t I know , me t wi th f i t g lasses to ma ke

any- th in g-accu ra t e t ab l e o f t he dec rem ent o f the fo r ce of t he d i l a t ed a i r; o u r p r esen tdes ign invi tes us to present the reader wi th that which fol lows, wherein I had the

ass i s tance of the sam e person tha t I tooke no t ice of in the form er chapter , as hav ingwr i t t en some th ing abou t r a r e f ac t i on : who m I t he r a the r mak e ment ion o f on t h isoccas ion, because whe n he f i r s t heard m e speak of Mr . Tow nley 's supposi t ions a bo utthe pro por t ion w herein a i r loses of i t s spr ing by di la ta t ion, he to ld me he had theyea r be fo re . . . made obse rva t i ons t o t t i e s ame purpose , which he acknowledged t oagree well en.ough with Mr. Townley ' s t h e o r y :162

I t h i n k ' t h a t t h i s q u o t a t i o n h a s b e e n s l i g h t l y m i s r e a d i n t h e p a s t , a n d y e t it

p rov ides an a ccu ra t e i nd i c a t i on o f T OW NE LE Y'S r61e i n t he evo l u t i on o f t he gas

law.

F i r s tl y , . BOYL E ackn owle dges t h a t T OWNEL EY po in t ed ou t t h e s i gn i f i cance o ft h e e x p e r i m e n t o n " h o w m u c h a i r d i la t e d i t s e lf lo s es o f i ts e l a s ti c a l f o r c e " . I t w a s

n o t s u g g e s t e d t h a t TO WN ELEY h a d d e r i v e d t h e l a w t o a c c d u n t f o r t h e e x p e r i m e n t s

on t he c omp ress io n o f a i'r. T hus , i t i s p ro bab l e t h a t BOYL E de r ive d t h e l aw f ro m

16, Ib id. , p. 1o2.



488 C. WEBSTER:

h i s e x p e r i m e n t s o n t h e c o m p r e s s i o n o f a ir , w h e r e a s T OW N EL EY p o i n t e d o u t t h a t

i t a ls o a p p l i e d to t h e e x p e r i m e n t s o n e x p a n s i o n .

B O YL E'S c o m m e n t s a b o u t T oW N E LE Y a r e a l so c o n s o n a n t w i t h o u r f o r m e re v i d e n c e . T O W N E L E Y h a d b e e n i m p r e s s e d b y B O Y L E ' S New Experiments Physico-Mechanicall, a n d h e h a d e x p e r i m e n t e d w i t h P OW ER o n t h e e x p a n s i o n o f a i r, a n d

f i n a l ly t h e y h a d r e d u c e d t h e se e x p e r i m e n t s t o t h e " p r e c i se e s t i m a t e " . T h i s h a d

b e e n s t a t e d i n t h e i r m a n u s c r i p t o f t 6 6 t a n d i t p r e s u m e d k n o w l e d g e o f t h e g as

l a w b y t h e a u t h o r s . I n t h e i r e x p e r i m e n t s t h e y r e a l i s e d t h a t t h e p re s s u r e of t h e

v o l u m e o f e n c l o se d a ir w a s e s t i m a t e d b y s u b t r a c t i o n o f t h e m e r c u r y l e v e l i n t h e

e x p e r i m e n t a l t u b e f r o m t h e b a r o m e t r i c p r e s s u re . T h e r e s u lt o f t h i s s u b t r a c t i o n

t h e y t e r m e d " t h e m e r c u r i a l c o m p l e m e n t " . T h i s w a s p r o b a b l y th e a s p e c t of t h e

e x p e r i m e n t p o i n t e d o u t b y T O W N E L E Y t o B O Y L E , w h o , i n t u r n , u s e d t h e t e r m

" t h e c o m p l e m e n t o f B r _m e rc ur yl to C [ b a r o m e t r i c p r e s s u r e 1, e x h i b i t i n g t h e p r e s -s u r e s u s t a i n e d b y t h e i n c l u d e d a i r " . a6a

S u c h a n e x p l a n a t i o n a s s u m e s t h a t B O YL E c a r r i e d o u t a c o r r e s p o n d e n c e w i t h

TOW NELEY , o r t h a t t h e y h a d a c o n v e r s a t i o n . T h i s l a t t e r p o s s i b i l i t y h a s b e e n i g n o -

r e d , y e t i t w o u l d e x p l a i n t h e l a c k o f s u r v i v i n g l e t t e r s b e t w e e f i BO YLE a n d T 0 W N E -

L EY . T OW NEL EY w a s a l s o a m o s t r e l u c t a n t c o r r e s p o n d e n t . I t h a s b e e n t h e l a c k o f

s u r v i v i n g c o r r e s p o n d e n c e a n d a b s e n c e o f t h e d i s s e r t a t i o n , m e n t i o n e d i n t h e

p r e v i o u s q u o t a t i o n , w h i c h h a v e c o u s e d m o d e r n w r i t e r s t o m i n i m i s e TO W NE LE Y'S

r61e in t he en un c ia t i o n o f t l~e Law. 164

F o r t u n a t e l y t h e P OW E R c o r r e s p o n d e n c e p r o v i d e s e v i d e n c e f o r T OW N EL EY 'S

a c t i v i t i e s d u r i n g t h e w i n t e r o f t 6 6 1 / t 6 6 2 . I n O c t o b e r 1 6 6 t , P o w E R w r o t e t o

C RO UN E t h a t TO WN EL EY w a s i n t e n d i n g t o v i s i t L o n d o n .

A s fo r t h e M a g n e t i ca l I E x p e r i m e n t s , I w i ll r e t u r n t h e m t o y o u b y M r . T o w n l e y

who i s f o r Lond on a t t he r e - se s s ion o f t he Pa r l i am en t . 16~

O n N o v e m b e r 2 7 t h h e w r o t e :

I b y t h e b e a r e r h e r e o f M r . T o w n t e y m y e v e r h o n o u r e d f r ie n d , r e t u r n e d y o u

t h o s e f e w m a g n e t i c a l o b s e r v a t i o n s I h a d l o n g s in c e m a d e . . . M r . T o w n l e y w h i l s t

h e e i s r e s i d e n t i n y e c i t y w i ll r e t u r n m e e a n y t h i n g f r o m y o u . I p r a y y o u d o e m e t h a t

h o n o u r , a s b e a c q u a i n t e d w i t h h i m : w e r e h e n o t a p e r s o n a b o v e m y C o m m i s s i o n Iw o u l d s a y s o m e t h i n g t o y o u o f h i m b u t I s h o u ld t h e r e i n p r e v e n t y e a b i l i t i e s a n d

judg em en t , wh ich i s soe acu t e , a s i t needs no t t he l ea s t hu r t o r i n t e rma t ion . 166

T OW N EL EY m e t C I~O UN E i n L o n d o n , a n d t h e l a t t e r w r o t e t o P OW E R.

L e t m e e t h a n k y o u i n t h e f i r s t p l a c e f o r t h e h o n o u r y o u d i d m e e i n t h e k n o w -

ledge o f so wor t hy a pe r son a s Mr. Tow nley , o f whom I sha l l no t bee so [ il leg ibl e J

a s to s a y a n y o t h e r t h i n g e t h e n t h a t I w i s h w e e h a d m a n y m o r e s u c h G e n t l e m e n a s h e e Y 7

A l t h o u g h t h e r e i s n o f u r t h e r e v i d e n c e a b o u t T OW N EL EY 'S a c t i v i t i e s i n L o n d o n

d u r i n g t h i s v i s it , I s u g g e s t t h a t h e a t t e n d e d s c i e n t i f i c m e e t i n g s a t t h e R o y a l

S o c i e t y , a n d t h e r e b e c a m e a c q u a i n t e d w i t h R OB ER T B OY LE . O n t h e b a s i s of t h e

e x p e r i m e n t s o f t 6 6 0 a n d t 6 61 h.e w a s a b l e t o a i d B O YL E'S i n t e r p r e t a t i o n o f t h e

168 Ib id ., p. 1 02.

1G4 In a l l acc oun ts w hich I ha ve seen i t has been assu me d t ha t TOWNELEY sug-ges t ed t he hypo thes i s i n a l e t t e r t o BOYLE.

165 HENRY POWER, le t t er to Crou ne, t6 Oc tob er, 1661, f . 26.166 HENRY P0WER, letter to Croulle , 27 N ov em be r, 1661, f . 28.167 WILLIAM CROUNE, le tt e r to HEN RY POWER, 1 M ar ch 1661/62, f. 30.



B o y l e 's L a w a n d t h e E l a s t i c i t y o f A i r 489

e x p e r i m e n t o n th e e x p a n s i o n o f a ir . T h e t r e a ti s e m e n t i o n e d w a s p r o b a b l y h i s

o w n a c c o u n t o f t h e e x p e r i m e n t s o f t 6 6 0 a n d t 6 6 t w h i c h h e h a d p e r f o r m e d w i t h

H EN R Y PO WER . U n f o r t u n a t e l y h e w a s a s r e l u c t a n t t o p u b l i s h t h is w o r k a s h e w a st o a d v e r t i s e h i s a c t i v i t i e s , a n d i t w a s e i t h e r l o s t o r p l a c e d i n t h e l a r g e c o l l e c ti o n s

o f m a n u s c r i p t s a t T o w n e l e y H a l l , w h i c h w e r e d i s p e r s e d i n 1 883., t o o u r n a t i o n a l

d is gra ce . 168

R OB ER T H OO KE h a s so f a r b e e n l i t t l e m e n t i o n e d i n t h e e x p e r i m e n t s t h a t l e d

t o B O Y LE 'S L a w , y e t h e h a s , i n s o m e a c c o u n t s , b e e n g i v e n a m a j o r r 6 1e i n i t s

e v o l u t i o n . 16~ H o w e v e r , t h e p r e v i o u s a c c o u n t s h o w s t h a t I I o o K E ' S c o n t r i b u t i o n s

w e r e in n o w a y e s s e n ti a l t o t h e e v o l u t i o n o f t h e L a w . H i s m o s t i m p o r t a n t w o r k

w a s in t h e t e c h n i c a l c o n s t r u c ti o n o f t h e a i r p u m p , b u t t h e e x p e r i m e n t s u s i n g t h is

p u m p d i d n o t l e a d to a q u a n t i t a t i v e e s t i m a t i o n o f t h e e l a s t i c i t y o f a i r.

I n t h e e x p e r i m e n t s d e s c r i b e d i n t h e s e c o n d e d i t i o n of New Exper iments h ew a s a g a i n r e f e r r e d t o o c c a s i o n a l l y . H e w a s p r o b a b l y t h e p er so r~ w h o a s s i s t e d

B OY LE i n c a r r y i n g t h e T o r r i c e ll i a n e x p e r i m e n t u p W e s t m i n s t e r A b b e y , a n d h e

a l s0 h e l p e d i n t h e e x p e r i m e n t o n t h e e x p a n s i o n o f a ir ; b u t BO YLE d o e s n o t m e n t i o n

h i m a s th e i n i t i a t o r o f t h e s e e x p e r i m e n t s Y °

M o s t i m p o r t a n t o f M1 h e v e r i f ie d th e e x p e r i m e n t o n t h e e x p a n s i o n o f a i r a n d

i n c l u d e d h i s a c c o u n t a n d T a b l e o f r e s u lt s i n t h e Micrographia, m h o w e v e r , i t

s h o u l d b e r io t e d t h a t h e w a s n o t m e n t i o n e d i n t h e History o/ the Royal Society as

p a r t i c i p a t i n g i n t h e e x p e r i m e n t s o n a i r p r e ss u r e, b e f o re D e c e m b e r 1 66 2, b y w h i c h

t i m e t h e m a j o r a d v a n c e s h a d a l r e a d y b e e n m a d e . 17~

O n m o r e p e r s o n w a s m e n t i o n e d i n c o n n e c t i o n w i t h t h e e x p e r i m e n t s o n t h e

e x p a n s i o n o f a i r ; t h i s w a s L o r d BRO UN CKEE. l la H e t o o h a d m a d e e x p e r i m e n t s ,

16s Catalogue o/ the Towneley MSS,.sold 27 Ju~e 1888, So theby , London , 1883 . - -

T h a t TO WN EL EY i n t e r c h a n g e d l e t t e r s w i t h B O YL E i s p r o v e d b y t h e l e t t e r s w r i t t e n

by TOWNELEY to OLDENBURG. F r om these i t i s app a re n t t ha t BOYLE had sen t

TOWNELEY a ba ro me te r i n t he su mm er o f t 672 , bu t t he re was some de l ay be fo rethe ap pa ra t us was u sed . - - My i n t e rp r e t a t i on o f TOWNELEY'S pa r t i n BOYLE 'S ex ~

p e r i m e n t s r e c e i v es c o n f i r m a t i o n i n o n e o f t h e l e t t e rs . - - " S i r . I t w a s s o m e s a t i s f a c t i o n

to me to f i nd i n ye Tra nsac t ions o f Ju ly y t ye hyp o the s i s (w ch Mr . Bo i l e was p l ea sed

to owne a s mine ) abou t ye fo r ce o f a i r e condens t and r a r e f i ed , do th succede a s we l li n d e e p e i m m e r s io n s , a s in t h o s e I m a d e t r i a l l of, a n d t h a t i r d o t h a d m i n i s t e r n o w t o

y e l e a r n e d m a t t e r o f f u r t h e r s p e c u l a t io n , a s f o r m e r l ie i t d i d t o m e o f w r i t i n g s o m efew thin gs, (of w ch I th en sho we d u nt o M r. Boile) . . ." R. TOWI~'ELEY o H. OI,I~EI~BIJ~G,

J a n u a r y 2 9 , t672/73, R o y a l S o c i e t y , G u a r d b o o k T , n o. 2 5.1~9 HOOKE'S r61e in th e fo rm ula t io n of BOYLE'S" La w ha s be en stre sse d b y R. T.

GIJNTI~ER an d E. N. I~A C. ANORAOE and m ore re ce nt ly by I . BERSrA~I~ COHEN (op. .c i t ., s ee foo tno te 138 ), bu t ca r e fu l co ns ide ra t i on o f t he ch ron o logy o f BoYT~E's ex -

p e r i m e n t s a n d e s t i m a t i o n o f t h e d a t e o f c o m p o s i t i o n o f H o o I ~ E 's a c c o u n t l a r g e l yinva l ida , te c la ims fo r t he p r io r i t y o f HOOKE'S work• See my fo r thc om ing a r t i c l e i n

Nature.170 t{. BOYLE 1'662, op. c ir ., p . 102.

m R. HOOKE, "Micrographia, Lon don , 1665, pp . 222 --22 5.~2 On Dec emb er i 0 th 1662, Hoo t~E dem ons t r a t e d t he i n f luence o f r educ ed p re s su re

o n a v o l u m e o f a i r a t a m e e t i n g o f t h e R o y a l S o c i e ty . O n J a n u a r y 2 8 t h t 66 2 /6 3 , h ea d a p t e d t h e e x p e r i m e n t , i n o r d e r t o m e a s u r e t h e i n f l ue n c e o f i n c r e a s e d p re s s u r e o n

a i r. A t 2 i n c h t u b e c o n t a i n i n g a i r w a s g r a d u a l l y i m m e r s e d t o a d e p t h o f 14 2 i n c he sin a deep g l a s s cy l inde r . The subsequen t dec rease i n vo lume was measu red . T . BIRCH,

I 756/57, op. c i r . , • vol . 1 , pp . 14 1-- t42 , 180--18 2. POWER an d TOWNELEY ha& per 7fo rm ed a s imi l a r exp e r im en t i n 1653 .

1~3 R . B OY LE, 1662, op . cir ., Works, vol. 1, p. 102.

Arch. Hist , ' l~xact.~eL, .Vol. 2 33



490 C. WEBSTER:

which, like those of HOOKE and BOYLE, were explained by TOWNELEY'S hypo-

thesiS: It is interesting that neither BROUNCI~EI~, HOOKE, nor BOYLE saw the

significance of their tables of results until it was pointed out by TOWNELEY.

BROUNCKER, unlike HOOKE, was in the committee appointed by the So'ciety to

examine the Torricellian experiment, and he was probably familiar with BOYLE'S

experiments before th ey were officially re co rd ed .

The successful formulation of the law of the elastici ty of air during tile autumn

of t66 t was the result of patient investigations of many authors; POWER and

TOWNELEY'S experiments had begun in t653, and BOYLE~S in t658/9. While

both the northern workers and BOYLE reach a similar hypothesis, their experi-

mental method differed c6nsiderably, and it is entirely equitable that BOYLE'S

work should be remembered as a model example of a sustained experimental

investigation of a quantitative physical problem. On the other hand, it should bepointed out that it was left to NEWTON to realise the wider physical significance

of the law of elasticity, while BOYLE and POWER were more interested in elast icity

as a qualitative phenomenon for use in arguments relating to the nature of air.

To them, the Law was an example of the fruitful application of experiment, but

it was subsidiary to their main interests and it occupied only an' inconspicuous

position in their works.

Finally, the last stages of this investigation indicate the value of'the Royal

Society in stimulat ing experimental research. It increased the number of investiga-

tors concerned with the problem, facilitated communication between widely

scattered workers and encouraged or even patronised the publication of theirresults.

Conc lus i ons

This present article has confirmed that BOYLE'S achievements in the study of

air pressure were the climax of a co-operative'enterprise in which he was the major

contributor, and that his concept of air pressure was greatly influenced by the

European researches. In this respect BOYLE'S position is similar to tha t of PASCAL

and TORRICELLI, who also benefitted great ly by the interchange of ideas with

other contemporary investigators, but each triumphed over their fellows ill their

ability to separate the experimentalaspect of the problem from general questions

of the philosophy of nature and even more in developing informal models of thestructure of air, the most important feature of which guided them into fruitful

experiments.

The works of PASCAL and BOYLE rei~resent theres ul ts of completed investi-

gations. In each case the section concerned with devising simple experiments to

support their hypotheses stands sharply apart from general considerations of the

plenist-vacuist controversy, and the emphasis of their works lies in the former

part. This contrasts with HENRY POWER'S work, in which the chapters start

with an experiment which is examined in order to shed light on his Cartesian

axioms. It is interesting that he presented his work in a form nearer to BOYLE'S

model after he had read the New Experiments, but his experiments were still

presented in a random manner, often inserted, for the sake of curiosity than for

relevance to a major physical problem.

The great advantages which BOYLE, PASCAL and TORRICELLI were able to

derive from other workers was probably increased by their presence in centres



Boyle ' s Law and the E las t ic i ty of Ai r 49 t

o f g r e a t s c ie n ti f ic a c ti v i t y . I t i s p r oba b l y no t c o i nc i de n ta l t ha t t he i r ma j o r w or ks

w e r e und e r t a ke n i n F lo r e nc e , P a ri s a nd L ondon , w h i c h w er e t he ve r y c e n t r es o f

t he de ve l op i ng sc i e nt if i c a c a de mi e s a nd w h i c h a t t r a c t e d t o t he i r i n f o r ma l me e t ingsma ny o f t he mos t f e r t i l e i n t e l l e c t s i n t he t h r e e na t i ons . I t ha s be e n no t e d t ha t

m a n y o f t he e xpe r i m e n t s on a i r p r e s su r e w e r e i na ugu r a t e d a t s uc h me e t ings ;

a nd t he r e w e r e ma ny a dva n t a ge s t o a c c r ue f r om g r oup s t udy o f t h i s pa r t i c u l a r

p r ob l e m.

F i r s t l y , ma ny o f t he e xpe r i me n t s w e r e r e l a t e d t o t he va c u i s t - p l e n i s t c on t r o -

versy which was ac t ive ly d i scussed a t the mee t ings , and th i s v igorous deba te

p r ov i de d a s ubs t r a t u m o f s pe c u l a ti on a nd c r i ti c is m ou t o f w h ic h t he e xpe r i m e n t a l

p r ob l e m mi gh t e me r ge . Ce r t a i n l y muc h o f t he d i s cus s ion w as a c a de mi c , b~ t e ve n

t he s c ho l a s t i c a u t ho r s o r i g i na t e d ne w e xpe r i me n t s a nd hypo t he s e s t o s uppor t

the i r ax ioms , and they were quick to see weaknesses in o the r hypotheses ore xp l a na t i ons .

S e c ondl y , g r oup e n t e r p r i s e w a s va l ua b l e i n ove r c omi ng the m a ny t e c hn i c a l

p r ob l e ms c onne c t e d w i t h t he s t ud y o f a ir p r e ss u re . G l as s a ppa r a t u s w a s r e qu i r e d

o f a f o r m a nd p r e ci s ion un kn ow n i n c he mi c a l e xpe ri me n t s . I t w a s ne c e s sa r y t o

e vo l ve me t hods o f p r oduc i ng l ong g l a s s t ube s o f un i f o r m bo r e , a nd p r oduc e

me t hods o f c a l i b r a t i ng t he m. T he c ons t r uc t i on a nd ' de s i gn o f t he a i r pump w a s

i t se l f d i f f i cu l t ; once i t was evolv ed spec ia l g las s evac ua t io n g lobes were requi red

and me thod s of prod uc ing a i r - t igh t s ea ls .

The t echnica l im per fec t ion s of the expe r ime nts of POWER and ToYgNELEY are

w i tne s s t o t he p r ob l e ms o f i nde pe nde n t i nve s t i ga to r s . E v e n i n t 661 t he y w e r eunab le to co ns t ru c t a g las s appa ra tu s t 33 fee t long , a l though th i s had b een achie -

ve d i n F r a n c e f o u r t e e n ye a r s be fo r e .

F ina l ly , the soc ie t i e s were a cent re for the publ i ca t ion of in format ion and

c on : e sponde nc e r a d i a t e d f r om t he m ; w h il e bo t h o f t he s e me t hods i mpr o ve d t he

d i s s e mi na t i on o f i n f o r ma t i on a nd c o - ope r a t i on be t w e e n ge og r a ph i c a l l y i s o l a t e d

groups : In addi t ion , a t a l a t e r da te , the soc ie t ie s were ab le to em ploy as s is t an ts ,

w ho e na b l e d t he m t o ove r c om e t e c hn i c a l p r ob l e ms , o r as in t he c a se o f }{OOKE,

became es sent i a l members of the groups .

T he i mp or t a nc e o f t he d i s t r ibu t i on o f i n f o r ma t i on by c o r r e s ponde nc e a nd t he

d i s t r ibu t i on o f ma nu s c r i p t pa mph l e t s w a s i mp or t a n t i n t he s t ud y o f a i r p r e ss u re ,

as i t was in many o ther spheres of s c ience . Such informat ion has of t en been

ove r l ooke d as t r iv i a l c omp a r e d w i t h pub l i s he d w r i t ings , ye t i t mus t be r e me m be r e d

t ha t o f t he nume r o us i nve s t iga t o r s me n t i one d a bove , on l y BOYLE and MERSENNE

were rap id to publ i sh the i r resea rches in a form which had genera l c i rcu la t ion .

E v e n w i t hou t pub l i c a t ion t he r e w a s s u r p r is i ng ly r a p i d a nd e f f ic i e nt t r a ns-

miss ion of knowledge. TORRICELLI'$ le t t er s to RlCCI were no t pub l ished un t i l

t663 , bu t MERSENNE had ex t ra c t s f rom the m sho r t ly a f t e r t i le 3} were wr i t t en in

-1644. Sir CHARLES CAVENDISH co m m un ica ted ROBERVAL'S car p-b lad de r exp eri-

me nt to PETTY in En gland in Apri l, t 648 , an d in Ma y of tha t yea r we f ind HART-LIB re lay ing th e same e xt r ac t to BOYLE. HAAK'S l e t t e r s show tha t the re was l i t t le

de l a y i n t r a n s mi t t i ng ne w e xpe r i me n t s f r om F r a nc e ~co . E ng l and a nd t ha t M ER-

SENNE was a key f igure in th i s in te rn a t iona l cor respond ence . In Eng land a t th i s

tkn e, SAMUEL HARTLIB was a n equ al ly en thu s ias t ic corre spon den t , a l though~ he,

l ike MERSENNE, l acked pu bl i c .suppor t for h is ac t iv i t i e s as an " in te l l igencer" .

33*



492 C. WEBSTER

However, once the Royal Society was founded, not the least of its activities

was~ the delegation of duties concerned with correspondence, an d this is illustra ted

by:the exchange of information between WILLIAMCROU~E and HENRY POWER.It is appropriate at this point to give a resum6 of the essential stages which

led from the initial understanding of the elasticity of air to the formulation of

BOYLE'S lawl before going on to resolve certain questions related to BOYLE'S

own work. The stages are given as a numerical sequence, and the dates refer to

the original investigations rather than the date of publication.

I. Associated with the "ocean• of air" hypothesis was the idea that the lower

layers of air existed in a s tate of compression; BEECKMAN (I 614 onwards), BALIANI

(1630), TORRICELLI(t64~).

2. Many experiments were devised which illustrated this compressibility of

air, and also its great powers of expansion. These were summarised by MERSENNE

(1644). Others were the vacuum-in-vacuum experiment and balloon experiments,

PASCAL (t647), and the carp,bladder experiment, ROBERYAL(t647/8).

3. It was realised that air enclosed in a vessel exerts a'force different from the

simple "weight resulting from its location at the bottom of the ocean of air".

This was visualized separately as the resistance to compression by an external

weight and the tendency to expand; NOeL (t648), ROBERVAL (t648), PECQUET

(165t), POWER (t653), BOYLE(t658/59).

4. This phenomenon was explained by the principles of mechanics, and a

conceptual model was utilised which stressed the spring-like nature of air, ROBER-VAL (i648), PECQUET (t651), POWER (t653), BOYLE (1660). PASCALproposed that

air was compressed in proportion to the pressure exerted on it, and ROBERVAL,

that the air's capacity of expansion decreased with is increase in volume.

5. The invention of the air pump by vol~ GUEEICKE (t654) and its improve-

ment by HOOKE (t658), allowed the experimental rarefication of air by BOYLE

(t659), ~vho attempted to measure the reduction in pressure and the accompany-

ing degrees of rarefaction. He sought unsuccessfully to reduce these results to a

law.

•6. Systematic measurements of the expansion of air, enclosed above mercury

in ROBERVAL'S apparatus, were made by POWER and TOWNELEY(April t66t).

The change in pressure was produced by the ascent of a hill. They deduced the

reciprocal proportionality between the volume of air and external pressure from

these experiments.

7. ~'he J~tube apparatus was evolved at 'the Royal Society me~etings (Sep-

tember 166t) by BOYLE and CROUNE. This .was used by BOYLE to produce tables

of the compression of air. He deduced tha t the spring o/air was proportional to

its density.

8. ROBERVAL'Sapparatus was adapted by BOYLEfor measuring the expansion

of a volume of air under reduced pressure. From the table of results TOWNELEYpointed out that the pressure O[ air was reciprocally proportion al to its ex pa ns ion

(December ? 166t). HOOKE verified the results of this experiments (16_6t/62).

• While the above summary indicates the major contributors to the discovery

Of BOYLE'S Law, it leaves unanswered the question of pr iori ty of discovery and



Boyle 's Law and the Elas t ic i ty of Air 493

t h e co r r ec t t it l e o f th e Law , p ro b l em s w h i ch a r e o f l i m i t ed i m p o r t an ce co m p ared

wi th tha t o f ob ta in ing an accura te h i s to r ica l accoun t o f d i scover ies re la t ing to

air pressure.There has a l ready been much d i scuss ion o f the mer i t s o f var ious t i t l es fo r

BOYLE'S Law, in which various combinations of BOYLE-HooKE-MARIOTTE-

TOWNELEYh av e b een p ro p o s e d Y 4 H o w ev e r , i t m u s t n o t b e o v e r l o o k ed t h a t t h e re

i s no law o f p r io r i ty in the namin g o f Laws , as there i s in bo tan ica l nome ncla tu re ,

an d t h a t i t is i n n o w ay t o b e s s u m ed t h a t t h e n am i n g o f Law s h a s an y h i s t or i c al

s ign i ficance . Th e t i t l es mer e ly se rve to fac i l i t a te as soc ia t ion wi th a par t i cu la r

genera l i sa t ion , and as such have a cer ta in psycho log ica l as s i s tance in t each ing .

I f t h e n a m e B O YLE b r in g s t o t h e s t u d en t ' s m i n d t h e r e l a t i o n sh i p b e t w een t h e

pressu re and dens i ty o f a gas, th en i t s pu rpose i s se rved , and i t i s o f l i t t l e im por ta nce

i f the l aw i s known by ano ther name in European coun t r ies . On ly i f there wass l igh t conf l i c t o f mean ing wou ld the re be s ign i ficance in the use o f one o r the o ther

n am e .

In t h e p reced i n g acco u n t i t h a s b eco m e o b v i o u s t h a t t h e Law w as t o s o m e

ex te nt realis ed b y PASCAL an d ROBERVAL, POWER an d TOWNELEY, in de pe nd en tly

and poss ib ly b efore BOYLE. This p laces BOYLE in a s imilar posi t ion to DARWIN

in the d i scove ry o f the p r inc ip le o f na tu r a l se lec t ion , fo r since the yea r o f publ i -

ca t ion o f the .Or ig in o[ Species, i t h a s b eco m e c l ea r t h a t h e h ad n u m ero u s an t i -

c ipa to rs . H owe ver , DARWIN'S ach ieve men t i s no t min im ised by these a n t ic ipa t ions ,

and ne i the r i s BOYLE'S . F o r BOYLE overshadow s th e o ther inves t iga to rs, bo th in

the compar i son o f h i s work wi th the i rs , and the u l t imate in f luence o f h i s work

on fu tu re genera t ions .

Fr om the ince p t ion o f h i s in te res t m a i r p ressu re , he rea l ised tha t there was

l i t t l e i m m ed i a t e p ro g re s s t o b e m ad e b y ex p e r i m en t s ap p l i ed t o t h e u l t i m a t e

p rob lems which had domina ted the d i scuss ions un t i l tha t da te and which had

indeed g iven r i se to mos t o f the exper imen ta l s tud ies .

Like PASCAL, he was con te n t to a pp ly expe r im en t to the consequences o f the

model o f a i r adop ted , a r id he exp lo red th is tho ro ugh ly and reserved cons idera t ion

of the more p ro found i s sues un t i l l a te r works . He devo ted equa l sk i l l to the exa-

mina t ion and re fu ta t ion o f fa lse hypo theses . T hus ther e a rose , ou t o f a subs t ra t um

of unresolved phi losophical prob~lems in h is work , an impress ive hypothet ico-

dedu c t ive ex p lo ra t io n o f the phys ica l p roper t i es o f a ir wh ich even tua l ly by passed

the ph i losoph ica l p rob lems , to become an independen~ inves t iga t ion o f na tu ra l

laws.

BOYLE ha d a fu rth er s im ilar i t y with PASCAL n h is sk i ll in devis ing ex perim ents ,

b e t t e r i n g h i m i n t h e p ro d u c t i o n o f e l ab o ra t e ap p a ra t u s an d i n t h e s y s t em a t i c

reco rd ing o f exper i men ta l resu l ts . Th is l a t t e r face t o f h i s work , wh ich was p rob-

ab ly one of th e few di rect m anife s tat io ns of BACON'S influence, as wel l of h is

own person a l i ty , reache d a c l im ax in the t abu l a r reco rds , o f a i r vo lumes a nd re la ted

pressu res .

1~ This article will not consider the contr ibution to the stu dy of air pressurema de by MARIOTTE,'~ince he relat ionsh ip be twe en his w ork and 1BOYLE'Shas al readybe en discu ssed th oro ug hly . See 13. Mc KIE , 1948, op. cir., pp. 269---272; W. S. JAMES,t928, op. cir., pp. 269--2 72; A. WOLF, A H$story of Science, Technology and Phil o-

,s°phy in the 16th and 17th Centuries, London, 1935, p. 235.



494 C.W~BSTER:

Dur ing the course o f h is ex per ime n ts BOYLE sub jec ted the e las t i c i ty o f a i r t c

a m o re t h o ro u g h ex am i n a t i o n t h an an y o t h e r i n v es ti g a t o r, an d s e l ec ted i t a s a

par t icu larl y s ignif icant conce pt from the works of GASSENI)I,MERSENNE,CHARLE-TON, and PECQUET.O f t h e se , o n l y t h e l a s t au t h o r h ad g i v en p ro m i n en t p l ace t o

the hyp o thes i s o f e las t ic i ty . Also f rom the ear l ies t exper im en ts he sou gh t to reduce

t h e p h en o m en o n t o a q u an t i t a t i v e l aw . To t h i s en d h e m ad e m o re e l ab o ra t e ex -

per !men ts than the o ther observers , and over two years he d id no t lo se s igh t o f

his object ive unt i l h is work was successful a t the end of t661.

He reco rded the f ina l s t ages o f h i s inves t iga t ions wi th the g rea tes t accuracy ,

and Was d i l igen t i n adm i t t ing ass i stance f rom o ther Eng l i sh sc ien t is t s ; perhaps

mos6 s ign i f ican t ly , these comp le te inves t iga t ions were p r om pt l y p ub l i shed in 1662.

The second ed i tion o f the New Experiments i s one ev idence fo r the backg round

to BOYLE'S work , wh ich m us t be exam ined in th e l igh t o f unpub l i shed reco rdsand co r respondence , bu t i t i s the so le means o f the fu tu re in f luence o f h is work ,

fo r i t had a wide c i rcu la t ion and i t s in f luence was no t su rpassed by o ther works

on a i r p ressu re . I t p receded the pub l ica t ion o f the wr i t ings o f PASCAL,TO~RI-

CELLI, POWER and HOOKE. Th us th is works s tan ds in a s imilar pos i t io n to the

Origin o] Species in i ts sphere, as the most defin i t ive and orig inal express ion of the

the ory o f the e las t i c i ty o f a ir .

The es tab l i shm en t o f BOYLE'S Law has cons iderab le ph i losoph ica l impo r tance

in the h i s to ry o f sc ience , because i t was the f i r s t numer ic a l l aw which i l lu s~a t ed

the func t iona l dependence o f two var iab le magn i tudes . Such laws p rov ide im-

por tan t i l lu s tra t ions o f the fa i lu re o f the idea o f causa t ion in the Ar i s to te l i an sense~s ince any change i ll vo lume i s s t r i c t ly conc urren t wi th the c hange in p ressu re ,

there be ing no jus t i f i ca t ion in as suming tha t the re la t io / i sh ip i s asymmetr ica l

o r sequen tia l . B u t BOYLE mus t n o t be accorded the pos i t ion o f p rop onen t o f the

concep t o f func t iona l dependence m oppos i t ion to the idea o f causa t ion i l l the

case o f h i s Law. His who le exper ience in exper im en ta l phys ics and chem is t ry

had been based on the p r inc ip le o f cause , and e f fec t ; and h i s descr ip t io f i o f h i s

exper iences l ead ing to the fo rm ula t ion o f h i s l aw i l lu s t ra te the same b ias o f

' l anguage . The in t roduc t ion o f a cause in the exper imen t l ed to a t empora l e f fec t .

Thus the g r ea te r the w eigh t " lean ing" u pon the a i r, the more " fo rc ib le i s i t s

endeavour of d i la ta t ion" . T he a i r " re s i s t s " the increase in pressu re . U pon th e

reduc t ion o f p ressu re the a i r " loses o f i t s e las t i ca l fo rce" . The inch o f a i r wh ich

was sub jec ted to reduced p ressu re "wh en ex pan ded to fo rce i t s fo rmer d imens ions ,

was ab le wi th th e he lp o f a mercur ia l cy l inder o f abo u t 15 inches to coun terpo ise

the w eigh t o f the a tm osphere , :wh ich the weigh t o f the ex te rn a l a i r g rav i ta t ing

upon the res tagnan t mercury was ab le to impel up in to the p ipe , and sus ta in

tw en ty e igh t inches o f merc ury , when the in te rna l a i r by i t s g rea t expansion ,.

had i ts spring too far deb i l i ta te d to m ake an y conside rable . . . res is ta nce :,,17~

I have s t ressed tha t BOYLE'S in i ti a l fo rm ula t ion o f h is l aw s ta t ed tha t the

p ressu re o f a i r was p ropor t iona l to i t s dens i ty , and indeed he used two d i f fe ren t

models and se t s o f causa l t e rms to descr ibe con t rac t ion an d d i la tion . Th is has a '

d i f fe ren t emphas i s to mos t express ions wh ich g ive the l aw as " the vo lume o f a

gas i s inver se ly p r0 /~or tiona l to the p ressu re e xer te d on i t " .

1'~5 1~.BOYLE, 1662, oio. cit., ,Works, vol. t, p. 162.



B o y t e ' s L a w a n d t h e E l a s t i c i t y o f A i r 4 95

T h e m o d e r n e x p r es s io n o f t h e L a w , u s i ng " v o l u m e " a s o n e o f t h e t w o v a r ia b l e s

h a s n o p h y s i c a l c o n n o t a t i o n a n d a l t h o u g h i t is t h e v o l u m e ( o r u s u a l l y l e n g t h o f

a c o l u m n ) o f a i r t h a t i s m e a s u r e d i n e x p e r i m e n t s ; t h e p r e s s u r e i s n o t d u e t o t h es p a c e i ts e lf . W h e n B O Y L E n o t e d t h e c o n t r a c t i o n o f a ir , h e s t re s s e d t h a t i t w a s

" r e d u c e d t o t a k e u p b u t h a l f t h e s p a c e i t p o s s e s s e d ( I s a y p o s s e s s e d , n o t f i l l e d )

b e f o r e " . T h u s t h e v o l u m e o f a ir w a s o f n o s i gn i fi c an c e , t h e f o r c e b e i n g c a u s e d

b y t h e i n c r e a s e d d e n s i t y a n d p o s s i b ly p h y s i c a l c o m p r e s s i o n o f t h e h y p o t h e t i c a l

p a r t i c l e s . T h i s e x p r e s s i o n a l s o i n d i c a t e s t h a t BOYLE, n t h e t r a d i t i o n o f PECQUET,r e g a r d e d t h e p r e s s u r e o f a i r as a d y n a m i c p r o p e r t y , i n th e t r a d i t i e u o f t h e f u t u r e

k i n e t i c t h e o r y o f ga se s.

T h e l a w a l s o a p p l i e d t o a i r o n l y , a n d t h e t e r m "gas" a t t h i s p e r i o d h a d n o

p r e c i s e m e a n i n g , a n d a s a p p l i e d b y VAN" H E LM O N T , g e n e r a l l y i n d i c a t e d a m i x t u r e .

B OY L E w a s h e s i t a n t a b o u t t h e p h y s i c a l c o n s t r u c t i o n o f a ir , a n d h e w a s g e n e r a l l yc o n t e n t w i t h t h e h y p o t h e t i c a l m o d e l u s e d b y P E C Q U E T ; l ik e R O B ER V AL h e

b e l i e v e d t h a t a i r' s p r o p e r t i e s o f r e s i s ta n c e w e r e c o m m o n t o o t h e r s p r in g s . T h u s a i r

i n c r e a s e d i ts r e s is t a n c e w i t h i n c r e a s e d p r e s s u r e , w h i l e " o t h e r s p r i n g s a r e s t r o n g e r

w h e n b e a t b y g r e a t e r w e i g h t s " . 176 T h i s c o n c l u s io n w a s o f c o u r s e w r o n g , b u t i t

i l lu s t r a t e s t h e i m p o r t a n c e o f t h e a n a l o g y i n f r a m i n g B O Y L E ' S c o n c e p t s o f t h e

n a t u r e o f a i r, a n d h i s e x p e r i m e n t s a p p e a r e d s o w e l l t o c o n f i r m t h e w e l l k n o w n

h y p o t h e t i c a l m o d e l.

F i n a l l y , B O Y L E'S i n i ti a l s t a t e m e n t a p p l i e d o n l y t o t h e c o m p r e s s i o n o f a i r,

a n d i t w a s o n l y s o m e m o n t h s l a t e r t h a t h e r e al is e d t h a t i t a p p l i e d to i ts e x p a n s i o n

w h e n h e a c c e p t e d t h e r e c i p ro c a l p r o p o r t i o n a l l y b e t w e e n t h e " e x p a n s iO n " a n dp r e s s u re . B u t t h e t e r m e x p a n s i o n w a s s ti ll m e a n t i n it s p h y s i c a l s en s e, o f " l a x i t y "

o r " d e b i l i t a t i o n " o f s t ru c t u r e .

I n t h e p r e s e n t a r t i c le I h a v e a t t e m p t e d t o i l lu s t r a t e t h e v a l u e o f c a r e f u l

e x a m i n a t i o n o f t h e i n v e s t i g a t i o n s w h i c h f o r m a b a c k g r o u n d t o B OY L E'S w o r k

a n d t o s h o w t h e g r e a t e x t e n t t o w h i c h B O Y LE a s s im i l at e d t h e e x p e r i m e n t a l a n d

h y p o t h e t i c a l n o t i o n s o f h i s p r e d e c e s s o r s d u r i n g t h e e m e r g e n c e o f h i s o w n t h e o r y

o f a ir p r e s s u re . I n r e a d i n g h i s w e l l o r g a n i s e d d e s c r i p t i o n s a n d c a r e f u l l y p h r a s e d

e x p l a n a t i o n s i t b e c o m e s a p p a r e n t t h a t h e w a s ab le t o d e ri v e t h e m a x i m u m b e n e f i t

f r o m t h e w o r k i n g m o d e l o f a i r w h i c h h e f a v o u r e d , w h i l e r e m a i n i n g c a r e f u l t o

r e s e rv e j u d g m e n t o n t h e u l t i m a t e p h y s i ca l v a l i d i ty o f t h a t m o d e l .

I t i s a ls o a p p a r e n t t h a t t h e f o u n d a t i o n f o # B O YL E 'S w o r k w a s l a id d u r i n g t h e

f i rs t h a l f of t h e s e v e n t e e n t h c e n t u r y , a n d a f t e r t 6 4 0 i n v e s t i g a t i o n s l e d c l e a r ly i n

t h e d i r e c t i o n o f t h e l a w . A t f i r s t t h e r e w a s a n u n d e r s t a n d i n g o f t h e e l a s t i c i t y o f

a i r a s a q u a l i t a t i v e p h e n o m e n o n , b u t b y t 6 4 7 t e n t a t i v e q u a n t i t a t i v e s t u d i e s h a d

b e g u n . F i n a l l y , i t w a s R O B E R T B O Y LE 'S g e n i u s ~v hic h e v a l u a t e d t h e c o n t r i b u t i o n s

o f d i v e r s e n a t u r a l p h i l o s o p h e r s a n d f r o m t h i s s y n t h e s i s b u i l t h i s o w n o u t s t a n d i n g

c o n t r i b u t i o n t o e x p e r i m e n t a l s c i e n c e .

D u r i n g t h e p r e p a r a t i o n o f t h i s a r t ic l e t h e a u t h o r h a s b e n e f i t t e d c o n s id e r a b ly

f rom t h e adv i ce o f P ro fes so r J . R .~:~AvETZ

o f t h e U n i v e r s i t y o f U t r e c h t . T h a n k sare a l so express ed to Pro fessor W. H . G. ARMYTAGE of the Un ive rs i ty of SHEFFIELD,w h o o r ig i n a ll y in t r o d u c e d t h e w o r k o f H EN R Y P O W ER t o t h e a u t h o r a n d t o v a r i o u smem ber s o f t he s t a f f o f t he C i t y G ram m ar Schoo l,. She f f i e ld and Mi ss Jo an H EPPEN -STALl. Of Cam br idge U niv ers i ty .

17G Ib id ,, p. 100 .



496 C. WEBSTER:

&ppend ix I

"Ae. P. de Rober val de Vacuo Narratio ad Nobilem Viru m Do mi num des

Noyers . . ." May -Ju ne, t648. Part f ive. 1~(From B. PASCAL, Oeuvres, Vol. 2, op. cit., pp. 325--328.)

When we demonstra ted t hat remarkable rarefaction Of ai r from our previous

experiment, to m any it seemed so incredible th at they would rather suspect someun kn ow n cause, th an agree unreser vabl y to our assertions, and I wished if possible

to free them from all doubts: I began to ponder ~n my mind, if perhaps there was

some body av aila ble to.us, which was bot h flexible and satisfactorily hold air. The

conven ient thing which came to my mind was the swim-bladder of the carp, because

it is quite flexible and is thought to have been given to this animal by nature for

the express purpose of conta inin g air: Now this bladder is a double structure and thetwo parts are connected, together by a narrow neck through which the air c ommuni-

cates. Of the two parts I selected the one which is more pointed and more nearlyApproaches the form of a cone, bec aus e the mem bra ne of th i s second part is far

stronger an d splits with greater difficulty.

This was now empt ied of nearl y all the air, so tha t the p roportion of air remain-ing in it was no t in fact 1000th part of that which it had formerly held~ A thread

was tied round the neck and i tied it so tight th at it could not let out its air, nor

adm it any. This was the n placed in the tube in which we had previously placed small

birds and mice, the superior part of which has the capacity of a'goose egg.

This being prepared, I made the experim ent using mercury, so tha t the spaceor seeming vacuum appeared as usual at the upper part of the tube which held the

bladder. Bu t to the complete astoni shment of tile bystanders, the bladder appeared

quite turgicl and distended, j ust as if .it was still inside the carp's belly, for, in fact,

th at very small am oun t of air which remained in it, liberated at last from compression,being in a position in which it was no longer compressed neither by our condensedair, no r by other s urroun ding bodies, had expanded itself to the size which the bladder

would permit. A nd with the inclination of the tube, the mercur y was sucked back,

the blad der bocame flacdid,, jus t as if its air was exhausted. Upo n re-erecting the same

tube, the mercury fell, the bladder expanded again.

At length, by vi rtue of perforating the pig's bladder, which closed the u pper

end of the t ube, using a fine needle, with but the mi nutest. hole so tha t air graduallypenetrated the tube, and tile air condensed around the bladder. The bladder deflated

and gradually subsided until it returned to the state which it had been in when it

was placed in the t ube. Otherwise7 at a not her time, if the hole was larger, the air

rushed in, in a moment , the deflation would occur more rapidly. 17s

All this confirmed our assertions about the air's rarefaction and condensationso that no one can any longer doubt it, but all openly assented -- except the few,

who have long been our adversaries, who now became a laughi ng stock. Neverthe -less, as it became obvious that they themselves were denying a thing so obviousnot 179 because the y t hough t, it u ntru e, bu t because the tr ut h of it had been firstly

~7) it has been pointe d out tha t this experi ment became very popular and was

widely quoted in support of tile concept of the elasticity of air. It was also relevantto the vacuist-plenist controversy. The passage is translated from the Latin, - -The ex pe ri me nt was described by various Fren ch writ ers; M. M~RSSNN~, Harmoni-corur~ libri X I I , Paris, 1648, " Lib er novus prae luso rius "; J. PECQUET, ExperimentaNoffa Anatomica, Paris, 1651, t661 ed. pp. 91~98; P. GASSENDI;Opera Om nia, Lyons,

1658, vol. t, pp. 214 --2t 5. In En gl an d it was described by POWER and BOYLE, Ex-perimental Philosophy t663, p. tl 7, New Experiments Physico-Mechanicall, London,1660, Works, vol. t, p. t2. The Ita lian trials of the experiment have be en described

by L. BELLONI, Scheime modelli della machina vivente nel seicento, Physis , t963,

6, pp. 262--k67.~7s "more rapi dly" is' inserted a t a poi nt where words are missing in the ma nu sc ri pt .~79 I have inserted "n ot " in the tex t to impr ove the sense of the sentence.



Boyle's Law and the Elastic ity of Air 497

detec ted by us. But this experime nt had been tried more than a hundred times, i n

.public and privately, in various ways and I had never failed.

Sometimes g~eat industry was applied to totally removing air from tl{e bladder,

and yet perfect evacuation was not possible, for there were always some smM1 airbubbles lying ill the folds of the "bladder. Nevertheless, the result of this was that

the bladder became less inflated in proportion doubtless to the rarefaction of thesurrounding air in the appar ent vacuum. 'Doubtless, by the rules of mechanics, t hat

air remaining inside the bladder cannot be more rarefied than the rarefied air inside

the tube which surrounds the bladder.

I also tried what would happen in the same place when the bladder was per-

forated. However, as soon as it was left in the space or apparent vacuuml it inflated

but at once steadily deflated, because the air inside it rarefied and finding an exit,

it expanded itself throu gh space in the tube or apparent vacuum, and the walls of

the me mbrane, not being held up by any air, fell together.

I experimented also, in the same way, using a bladder full of our condensed air

and properly tied up, and that air in the space or apparent vacuum being held backonly by th e me mbr ane of the bladder , pressed by force on all sides, see king to dilate,

so that it burst some of them, principally around the thread which tied them, cer-

tainly because the membrane was weakened at that point..

Append ix I I

"Ae. P . de Roberv al de Vacuo Narrat io ad Nobilem Virum Do min um des

Noye rs . . . May-J une, 1648; part three, is°

(From B. PASCAL, Oeuvres, vol. 2, op. cit., p. 313--318.)

I so refilled a tube, three feet or a little less in length, with mercury so thatone and a half spaces were !eft, which were filled with our air. The tu be was the n

inverted and its mouth immersed-in the mercury of the dish, the one and a half

inches of air ascended into the upper part, above the mercury. Nor did there appear

any space there other than the apparent vacuum, into which there arose bubbles

out of the mercury, as was seen upon closer scrutiny. They were not in large numbers

as in the above experiment, but Some were somewhat larger; nor indeed was there

any doubt that a large number ascended, but we were.not able to see them. Of course,

they were not seen in the mercury because it is opaque, or in the space or apparent

vacuum, because there was nothing of distinct colour between the bubbles and this

space. This was afterwards confirmed by suddenly admitting two one and a half

inch .portions, one of water, the other of air, into the tube besides the mercu ry, by

which means the ascension of tile innumerable bubbles of air iato the water --wereeasily seen. And indeed, in both these experiments, either ~ith the air alone, or

with both air and water, above the mercury, a great change with regard to the mer-

curial level appeared. For, in t hat case a depression of the custom ary level by wholly

four inches is seen, so tha t it did not ascend to th e said he ight of two fe et Esic. .

And, howe ver oft en t he same experiment:, was re peat ed ir~ .the same kind of tube,

the same result appeared, either with air alone, or with the admittanc6 of water

besides this air. Though, with the admission of water alo~le there was not the same

result. Moreover, in other tubes, the shorter they were the lowerthe mercury became,

while the longer it went higher, to the ex ten t howeve r tha t once some measure had

been admitted, whatever the height of the tube, the mercury never reached its cus-

tom ar y hei ght of 2.7/24ths. feet. However, wh en I rea soned using the laws of mechanics,

about, the induce ment of such a depression of mercu ry by air, it has not been possibleto take up a ve ry satisfactory POsition or prov ide a be tter explana tion accordingto the laws of nature, tha n if it were agreed that the air spontaneously and of itself

became rarefied in the tube, (although I hav e tried other e xplanat ion s in my first

Narration) in such a way th at t he app arent vac uum occupies the whole of th a t

1so This passage is tra nsla ted from th e Latin.



498 C. WEBSTER :

space; yet is not true to say that the whOle of the air's whole force towards rarefaction

is exhauste d. The same air, while seeking to fill the whole space exerts a pressure

in all directions, on the adjacent bodies, the tube keeps in tile particles from all

ot he r directions, me rcury being the only one of them tha t can give way towardstile lower part of the tube. Moreover this explanation must be adopted: tha t the

air which we respire only possesses such force towards' dilatation and rarefaction

as is equal to the power of the natural element compressing or condensing it. Besides

which, this also agrees with the laws of nature itself and applies in all other bodies

which natur e has gr anted powers of spring, as in bows and inn umera ble oth er ex-

amples. All of which bodies, as long as they are compressed by force, but not extended

beyond the limits of their own power, never cease to resist. They are carried by an

innate force of resilience, which is the same as that force with which they are drawn

or impelled by othe r bodies. So, at t he be ginning of its rebound t he force is at its

greatest, then it gradually grows less and less, and finally disappears altogetherwhen the body has returned to its normal state. In the same manner, air, included

in the tube, as long as the tube remains closed at both ends, is only compressedand condensed to the extent of the force of the natural element exerting pressure.

on our air; and for tha t reason th e included air, by an equal and oppo site force,

resists such compression, attempting to become dilated to acquire a larger space

than it does in nature. For, the air included in the tube is not less condensed and

compressed than that outside, because, once it has been compressed and condensed,

it does not hereafter obtain any freedom to dilate and rarefy. Nor is the same air

compressed be yond its strength, for..~t is consistent with expe rience tha t air is capable

of much greater compression and condensation. This happens daily in numberlessways, but especially in brass pipes with t he app licati on of a plunger. And so, with

its strength unimpaired, it continually tends to rarefy and in fact it does so immedi-

ately, the very moment it is set free. And this is what happens when the lower end

of the tube is enclosed within the mercury of tile dish and a free descent is left forthe mercury of the tube into the same dish. For then, the air which was compressed

in the upper part of the tube and atthe sametime exerted a pressure in all directions,

is bound to rarefy upon the wit hdr awa l of the mercury. At the beginning of its

expansion it had a great power of rarefaction, because, one must suppose that it

was condensed by the force of pressure of the entire natural element. Then, its force

gradu ally re laxes because it is less and less compressed .and condensed, so that, one

and a half inches, af ter r arefyi ng thro ugh 6 or 8 inches of space, is able to move. to

tile extent of only four inches of mercury, although at the start of its rarefaction

it easily displaced 27 [inchesJ. And hence, in a tube three feet long or a little less,

in which the air rarefies through 6 or 8 inches, the mercury is driven out by that

air, only to the extent of about four inches below its accustomed height of 2.7/24ths.

feet, Moreover this effect is grea ter i n shorter, and less in longer tubes : becauseevidently, in shorter tubes, it Emercury~ is forced down by a smaller space, the air

rare fying less ; and further, the air in dilating holds grea ter forces and for that reason

it has more power of expansion and displacement of mercury, and vice versa.

I know that there remains quite a considerable doubt in some peoples' minds

when I sa y tha t greater forces are required .to drive down to the gr eater ex tent below

its appointed height of 2.7/24ths. feet; and a smaller force to drive it down less,for they will imagine that no force at all is required. Under the hypothesis which

we hold, air rarefies spontaneously and freely expands into the space left by themercury and seeks to occupy an ever gr ea te r space. By which manner, it seems

likely that the mercury would discharge itself completMy by its innate gravity, from

the tube into tile vessel, and that air is dilated by its own nature throug h the whole

of the same tube and it would occupy a longer tube if longer were provided for it.But this difficulty will "easily be remove d by anyone with a moder ate knowledge

of mechanics, if he reflects on that force by which the elementary parts of the wholeof nature are mutually compressed to constitiate a single elementary system. I con-

sider t ha t this I force, Which we com monl y .call gravity, and which vul gar philosophyc6nsiders is just like simple gravity, is indeed more substantial, like a mutual pres-



Boyle's Law and the Elastici ty of Air 499

sure or oscillation of all parts together. Once it has been agreed that gravity in this

lower re gi on of the air, or at the surface of the earth, is as great as the weight of

2.7/24ths. feet ill altitud e of mercury, and tha t the t enden cy to unifica tion between

the higher and lower parts of the elementary system is in the lower regions 6f theair, assumed to be eq uiv ale nt to the weight of the heig ht of 2.7/24ths. feet of mercury ,

or the weight of about 31 feet in height of water, which am ou nt st o the same thing.Once these two points have been conceded in their entirety, if there is no impediment ,

the mercu ry rises to a height of 2.7/24ths. feet, or water to a height of ab out 31 feet.Thus finally, the parts of elementa ry natur e form all equilibrium, which is the aimof the whole of natu re, and when tile equilibriu m is distur bed, these parts will im-

mediately be recalled, by their natural effort towards their innate endeavour. Butas a matter of fact, if besides mercury or water, there be admitted into any part

of the tube some of our compressed and condensed air, as we have stated above,

this air obtains its freedom and all its parts recoil and become rarefied and driveout the m ercu ry or water, which for th at reason will be depressed below the aforesaid

height, either more or less, according to the air itself possesses greater or lesser powe rof rarefaction.

Append ix I I I

J. PECQUET, Experimenta Nova Anatomica,Amst erd am, 1661, pp. 106--109. lsl

"Water only compresses the Terraquaecous Globe by vir tue of i ts weight,

but air not only by vi r tue of i ts weight but als0 by Elater ."

Let this be firmly and invi ncibl yestablished by these easily performed experiments.

A cylindrical glass tub e AB, exceeding a litt le less th an three feet in lengt h and .ifyou wish, about four lines in diamater. The end B is hermetically sealed, that is the

glass is itself compl etely'c losed up, t he other end A bei ng left open. Mercury is pouredinto the whole tube with the exception of seven inches CA~ water occupying the

residual space. Tile mouth is completely closed by the finger, and the tube is theninverted, when tile lighter water changes places with the mercury, and at length

condensed to the other end t3. The tube was then immersed in the rest agna nt mercury-

prepared in the vessel D, while sill being supported by the finger, so that when the

finger was swiftly withdrawn the metal flowed down out of the tube. That remaining

.in the t ube is tile mercury cylinder AE. It rests, not to the usual height of 27 inchesabove the surface of restagnant liquid, but is actually lowered by about 6 lines,on account of the cons tant pressure of water, which was itself permane ntl y 7 inches.

It was in fact no wonder that water was in this proportion to mercury since sevenand a half inches of the lat ter are abou t equal in weight to half an inch of the former.

Hence it is plainly evident that water exerts only the force by weight but notby elater; just as the mercury is affected inside the tube, so it weighs down on the

surface of the earth's mass.

But, on the other hand, air possesses th at virtu e to a great extent, for if thisexperimen t is repeated, not with water; but with air filling the seven residual inches CA.Tha t Js the t ube is filled up to BC with mercury, an d to the mout h A with seven

inches CA, which are alone filled with air and then close by the finger. Next, invert

and immerse in D. You will be surprised by this contrivance, the mercury cylinder AEfalls more than seven inches below the twenty-seventh. So it is evident that the

adjac ent merc ury was no.t forced down as much by weight as by the strongest dat er ;and it is that thus the Terraqnace0us Globe is compressed by air.

At this point I must P0ilit out that where it has brought to rest above 20 inchesof mercury, by reaching the 17th inside the tube, just as is frequently described inthe experiment on the cause of variation of level in the thermometer tube, whichfluctuations are in proportion as the air is at one time rarefied and at another timecondensed:

lsl This passage is translat ed from the Latin.



500 C. WEBSTER

Appendix IV

H. POWER, Experimental Philosophy, London, t664, 1663, pp. 101-~-103.

Pecquel (who I think follows Roberuallius therein) i ngeni ously conceives, th atthe whole mass of Ayr hath a Spontaneous Eleter, ornatural aptitude in in self todilate an d expand it self upon the removal of all circu mambi ent obstacles (which

he calls the Elastical motion of that Element) so that the particle[s] of Ayr may be

understood to be as many little Springs, which if at liberty, and not bound and

squeezed up, will powerfully, strongly, and spontan eously dilate an d stretch out

themselves, not onely to fill up a large room, but to remove great bodies- 'So that

he compares this .vast El eme nt-o f Air, circumfused about this terraqueous Globe,to a great heap of Woollfleeces or Sponges, piled one upon another, the superior

particles of the Ayr pressi ng the inferior, and hindring their con tinua l tend ency to

a self-dilatation; so that all the particles of thisAtmosphere (especially the inferioursort) strive a t all times to expand and dilate themselves: and when the circumresist-ency of other contiguous Bodies to them is removed, then they flye out into their

desired ex pansi on (or at least will dilate so far as neighbou~ing Obstacles will permi t:)

Jus t like the Spring of a Watch (which if the String be broke, presently fifes out

into its fullest expansion which Elastick motion in the Ayr then ceases, when it

comes to all aequilibrati on with those circumj acent Bodies tha t resisted it.

Tha t this is not onely an Ingenious Hypothesis, but tha t .there is much of reality

a nd t r ut h in it, I thi nk our following Expe rime nt will to safety of satisfaction demon-

strate.

Onely we differ-from Pecquet in the strict notion he hath of Rarefaction and

Condensation, which he supposeth to be performed without either intromission or

exclusion of any other extraneous Body whatsoever. Now how Ayr or any other

Body should diminish or augment its Quantity (which is the most close and essentialAttribute to Bodies) without change of its own Substance, or at least without a

reception or exclusion of some other extrinsecal Body, either into~ or out of the

Porosities thereof, sounds not onely harsh to our ears, but is besides an unintelligible

difficulty.

No w though we cannot by Sensible and Mechanical Demonstration sho w h ow

any ne w Substance or Subtler matter (than Ayr is) which enters into the Tu be to

replenish that seeming vacuity, and to fill p the aerial interstices (which mus t needs

be considerable in so great a self-dilation), ye~ w e must (considEring the nature of

rarefaction aforesaid) be forced to believe it: and perhaps some hap py Experimenter

hereafter may co me to give us a better then -this Speculative and Metaphysical

Evidence of it.

That the hollow Cylinder in the Tube is not onely fi]l'd up with the dilated

particles of Ayr, but also with a thin Aetherial Substance intermingled with them:

I. Let us suppose therefore (at random if you please) that there is a thin subtle

aetherial substance diffused throughout the Universe; nay, which indeed, by farr

the greatest thereof: in which all these Lumino us and Opace Bodies (I mean the

Starrs and Planets) with their Luminous and Vaporous Sphaeres (continually eff-

fluviating from therh~ do sw im at free and full Liberty.

2. Let us conmder that this aether is of that Subtil and Penetrative Nature,

that like the Magnetical Effluviums, it shoots it self through all Bodies whatsoever,

whose small pores and interstices are supplyed and fill'd p with this aetherial Sub-

stance, as a Sponge with water.

3. Let us add to the former Considerations, that the Ayr hath not onelv a strong

Elatery of its own (by which it presses continually up on the Earth, and all Bodies

circuminclosed by it) and it also ponderates, and is heavy, in its own Atmosphere.

Bu t because I am resolved you shall take nothing u po n the trust .and reputation

of the best Authour, ~ake this Experiment to prove the Ayr's ~ravitatio~ (in p~opr~o

Loco) as the vulgar Philosophy cals it.



Boyle's Law and the Elastici ty of Air 501

Appendix V

R.]3oYLE, New Experiments Physico-Mechanicall, London, t660; Works,

London, 1744, Vol. I. p. 8.

For the more easy understanding of the experiments triable by our engine, Ithought it not superfluous nor unreasonable in the recital of this first of them, to

insinuate that notion, by which it seems likely, that most, if not all of them, will

prove explicable. Your Lordship will easily suppose, that the notion I speak of is,

th at there is a spring, or elastical power in the air we live in. By which tRaz~9 orspring of the air, t ha t which I me an is this; th at our air eith er COl~sists of, or at least

abounds with, parts of such a nature, that in case they be bent or compressed by

the weight of the incumbent part of the atmosphere, or by any other body, they

do endeavour, as much as in them lieth, to free themselves from that pressure, by

bearing against the contiguous bodies that keep them bent; and, as soon as those

bodies are removed, or reduced to give them say, by presently unbending and stretch-ing out themselves, either quite, or so far forth as the contiguous bodi es th at resist

them will permit, and t hereb y exp anding the whole parcel of air, these elastical

bodies compose.

This notion may perhaps be somewhat further explained, by conceiving the air

near the ear th to be such :a heap of little bodies, lying one up.on another, as may

be resembled to a fleece of wool. For this (to omit other likenesses betwixt them)

consists of many slender and flexible hairs; each of which may indeed, like a little

spring, be easily bent or rolled up; but .will also, like a spring, be still endeavouring

to stretch it self out again. For though both these hairs, and the aereal corpuscles

to which we liken them, do easily yield to external pressures; yet each of them

(by virtue of its structure) is endowed with a power or principle of self-dilatation;

by virtue whereof, though the hairs may by a man's hand be bent and crouded closer

together, and into a narrower room than suits best with the nature of the body;

yet, whilst the compre ssion lasts, ther e is in the fleece the y compose an e ndea vour

outwards, whereby it continually thrusts against the hand that opposes its expansion.

And upon the removal of the external pressure, by opening the hand more or less,

the compressed wool doth, as it were, spontaneously expand or display it self towards

the recovery of its former more loose and free condition, till the fleece hath either

regained its former dimensions, or at least approached them as near as the compressing

hand (perchance not quite c~pened) will permit. This power of self-dilatation is some-

what more conspicuous in a dry spunge compressed, than in a fleece of wool. But

yet we rather chose to employ the latter on this occasion, because it is not, like a

spnnge, an e ntire body~ b ut a numbe r of slender and flexible bodies, loosely compli-cated, as the air it self seems to be.

There is yet another way to explicate the spring of the air; namely, by supposing

with that most ingenious gentleman, Monsieur Des Cartes, that the air is nothing

but a congeries or heap of small and for the mos t part) of flexible particles, of severalsizes, and of all kind of figures, which are raised by heat (especially that of the sun)

into that fluid and subtle ethereal body that surrounds the earth; and by the restless

agitation of that celestial matter, wherein those particles swim, are so whirled round,

that each corpuscle endeavours to beat off all others from coming within the littlesphere requisite to its motion about its own centre; and in case any, by intruding

into th at sphere, Shal l oppose its free rotation, to expel or drive it away: so that ,

according to this doctrine, it imports' very little whether the particles of the air have

the structure requisite to springs, or be of any other form (how irregular soever)since their elastical power is not made to depend upon their shape or structure, but

upon the vehement agitation, and (as it were) brandishing motion, which they receivefrom the fluid aether, that swiftly flows between them, and whirling about each of

the m (independe ntly from the rest) no t only keeps those slender aereal bodies separate dand stretched out (at least, as far as the neighbouring ones will permit) which other-

wise, by reason of their flexibleness and weight; would flag or curl; but also makes



502 C. WEBSTER: 13oyle's Law and the El as ti ci ty of Air

them hit against, and knock away each other, an d conse quently require more roomthan that, which if they were compressed, they would take up.

By these two differeing ways, my Lord, m ay t he springs of the air be explicated.

But though the former of them be that, which by reason of its seeming somewhatmore easy, I shall for the most part make use of in the following discourse; yet amI not will ing to declare perempt oril y for either of them agai nst the other. And indeed,though I have in another treatise endeavoured to make it probable, that the return-

ing of elastical bodies (if I may so call them) forcibly bent, to their former position,may be mechan ical ly explicated; yet I mu st confess, tha t to deter mine whether themotion of restituiti on in bodies proceed fr om this, tha t the p arts of a body of a

peculiar structure' are put into mo ti on by the bendin g of the spring, or from the

ende avou r of some subtl e ambi ent body, whose passage may be opposed or obstructed,or else its pressure uneq ual ly resisted by reason of the new shape or magni tude, whichthe ben din g of a spring may give the pores of it: to de term ine this, I say, seems to

me a m at te r of more difficulty, t h e n at first sight one Would easily imagine it.

Department of Philosophy

Leeds University

(Received February 26, 1965)

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Boyle Elastic