Scientist in Merck & Co.'s Research and Develop- conjunction with use of Wenner Potentiometerment Division is watching galvanometer scale in in measurement of molecular weight.

Merck uses Wenner Potentiometerin measuring molecular weights

Merck & Co. chemists determine molecularweights of vitamins, hormones, antibiotics, andother organic substances by the exacting "boilingpoint elevation method". Precision of this deter-mination depends upon the accuracy with whichminute temperature differences can be measured.To obtain the ultimate in precision, therefore, theMerck laboratory uses a Wenner thermocouplepotentiometer. With this instrument Merck re-searchers obtain temperature difference measure-ments consistent to within 4-0.0002 C.

The Wenner Potentiometer is the ideal instru-ment for making these highly precise measurementsof minute voltage. On its low range the instrumentis calibrated from 0 to 11,111 microvolts, in stepsof 0.1 microvolt, and has a limit of error of only4(0.01%7 + 0.1 microvolt).For a description of the instrument, see Cat.

EH22-33A(1). Write Leeds & Northrup Co., 4926Stenton Ave., Phila. 44, Pa.

- SUtING INSTRUMENTS TELEMETERS AUTOMATIC CONTROLS HEAT-TREATINC rURNACES

Jrl. Ad EH22-33A-242(la)

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- #1 NEW BOOKSDISEASES OF VEGETABLE CROPS

By JOHN C. WALKER, University of Wisconsin. McGraw-Hill Publications in the AgriculturalSciences. Ready in February

A text and reference for courses in horticulture and plant pathology, this book covers completely theknown facts concerning the diseases of such vegetables as asparagus, bean, celery, onion, etc. Eachdisease is discussed by a consideration of symptoms, causal agents, the cycle of development, andmethods of control. A list of references is included.

LIMNOLOGY. New 2nd Edition

By PAUL S. WELCH, University of Michigan. McGraw-Hill Publications in the ZoologicalSciences. Ready in Januarv

A thorough revision of a well-known book which deals with the biological productivity of inlandwaters and its underlying causes. The book is general, without emphasis on any area, and suitablefor text and reference use. Much new material has been added.

BODY DYNAMICSBy ELEANOR METHENY, University of Southern California. McGraw-Hill Series in Health Edu-cation, Physical Education, and Recreation. Ready in December

An elementary text on the fundamentals of efficient posture and movement and the uses of exercisesin improving body efficiency. Practical and inspirational, the book develops the theme of maximumresults with minimum effort in relation to the expenditure and conservation of energy.

SHORT WAVE RADIATION PHENOMENABy AUGUST HUND. Radio Communication Series. In press

This new book offers an up-to-date presentation of short wave radiation phenomena with many use-ful applications which play an important part in modern radio communication and in branches whereelectromagnetic waves are used for guiding objects. Gives practical applications together withclassical and more recent propagation theory.

Send for copies on approval

McGSA V BOO. COMPA

2 SCIENCE, VOl. 114

DETERMINATIVE BACTERIOLOGYLABORATORY MANUAL

by Thomas H. Lord, Kansas State CollegeThis new manual was written for a course inbacterial identification. It is compiled to meetthe needs for a step-by-step procedure foridentifying the common members of the Eubac-teriineae encountered as unknown organisms.

The manual leads the student through the vari-ous. progressive steps of isolation, purification,morphologic study, cultural study, and bio-chemical study of an organism. Designed forone semester of three two-hour classes per week.

PRICE $2.25

Send for an On-Approval copy

T~~~~~~~~~

Measures 20Micro-microlumensto 20 Lumens

ofScattered Light

FOR THE MEASUREMENT OF:ILDroplet size of aerosols . .. Purity of proteins and other colloids a 6. ..t Rate of chans e of moleculesizein solution . . . Particlesize and concentration in dispersed systems . . . Concentration 1 _ 0>Xand size of undissolved particles ...Opacity of almost-opaque*X1 X A

materials . . . Molecular agregation in antigen-antibody reactions * <.-. . . Microfluorescence in dilute solutions . . . Depolarization,. -turbidity, and dissymmetry of high-molecular-weight solutions . . . s 5 5 -dLight reflectance of dark surfaces . . . Minute precipitation,flocculation, and crystallization . . . Molecular weight of highpolymers in solution . . . Scintillation efficiency of nuclear-radiation-sensitive crystals and phosphors . Microchemicalturbidity analyses. F U

FEATURESExcellent sensitivity. Compact . . . accessible. Built-in stable d-c. amplifier.

Completely a-c. operated. Fully accessible interior. Maladjustment of the controls cannot

Has outlet for recorder operation. Comparisons of light intensities damage the unit.Internal electronic stabilization. indicated as decimal percentages. Removable slit and optical systems.

WRITE FOR BULLETIN 2182-K

AMERICAN INSTRUMENT COMPANY, INC.S.ce. 19

SCIENCE, VY1. 1144

THE MICRO-FLOW REGULATOR

Here is a new clamp for regulation of flowthrough plastic or rubber tubing, O"- 38.

Adjusts by smooth-acting ratchetwhich permits minute changes offlow for infusions etc., with ready

return to a former rate.One "click" equals.00078" movement of thepressure plate.

Constructed entirely ofstainless steel, with the

traditionally fine workmanshipof the Harvard ApparatusCompany, Inc. The cut showsactual size.

From stock, $5.00

Catalogue and price-list sent on request.

THE HARVARD APPARATUS COMPANY, INC.Dover Massachusetts

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* Required equipment in industrial laboratories, universities, research anddevelopment companies.

L * Accepts alluniversal stages.* Micrometer fine adjustment on double ball bearings (0.001 mi

* Anastigmatic tube analy.er.* Objective changing device and centering device.

* Focusable Bertrand auxiliary lens.* Rotating object stage on ball bearings.

Another of the famousLeitz microscopes...recognized everywhereas the finest microscopesmade anywhere.

For further information write Dept. 1O2SC.

E. LEITZ, Inc., 304 Hudsson Street, New York 13, N.Y.

LEITZ MICROSCOPES * SCIENTIFIC INSTRUMENTS * BINOCULARSLEICA CAMERAS AND ACCESSORIES

November 30, 1951 5

the cmicroscope lamp

4 NUCLE4

z i DERI'

Adenosine TriphosphateAdenineAdenine SulfateAdenylic AcidAdenosineCosymaseCytidineCytidine SulfateCytldtvle Acid

Deoyrlbonucleic AcidFructosew6-Phosphate

(Barlum)Glusose.l-Nhosphate(Potasium)

GlutationeGuanineGuann HydrochlorideGuanosineGuanylHc AcidHexase Diphosphate

OPar

IVA

'ROTEINS

id

kTIVES

HypoxanthineInostineIron NucleateManganese Nucleate6 Methyl UracilNucleic Acid (Ribose

Nucleic Acid)Protamine NucleatePhosphoglyceric Acidd RiboseSodium NucleateSodium DesoxyribonucleateAmmonium UndylateThymilne (S Mothyl

Uracil)UracilUridineUridylic AcidUramilXanthineXanthosine

Write for Revised Catalogue S 950 Listinga Complete Selection of Over 500

Important Biochemicals

NUTRITIONAL BIOCHEMICALS CORP.21010 Miles Avenue * Cleveland 28, Ohio

A

_CHECK THESE POINTS THAT SPELL SUPERIORI'

1. An unusual wide range of driving speeds without the dis-adv3ntages of gear shifting.

2. Immediate change of speed without lag-tracing is con-tinuous.

3. The number of possible speeds is infinite.

4. Speed changes made through dual controls-directly visibleand accessible.

5. Special automatic weight adjustment-an idler drum tocompensate for variations in temperature and humidity.

SCIENCE, V1. 11J.4

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( I

ACTH * Growth * GonadotropesEstrogens * AndrogensCorticoids Progesterone

Others

HYPOPHYSECTOMIZEDRATS

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-3 I1---

I._-I....

FOR A MELODIOUS CHRISTMAS-Wonderful NEWrecordings ofhird

Made for theAlbert R. Brand Bird Iir Son sSong Foundation,

Laboratory of VOLUME TWO

Ornithology,ACornell University

FIVE new twelve inch vinylite records bringthese new bird songs right into your home.These recordings, made in natural habitats,feature North American warblers, birds, ofgardens and shade trees, of the roadsides, oflakes and marshes.The bird songs are spaced on the five big

records so that you can find the one you wantquickly, and an announcer identifies each birdbefore it sings.

A FEW OF THE MANY BIRDS THAT SINGFOR YOU IN THIS ALBUM:

Bluebird LimpkinBronzed Grackle Yellow-headedTufted Titmouse Blackbird

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Coot

Five Twelve Inch Vinylite Records, TenSides, in a Decorative Album. For 78 r.p.m.machines. $10.50

And don't forgetAMERICAN BIRD SONGS (Volume I)

Six ten-inch vinylite records, twelve sides. "Of im-.mense interest and value to every bird lover."-Science Review $8.50 postpaid

Mail This Coupon Today!

To: COMSTOCK PUBLISHING ASSOCIATES124 Roberts Place, Ithaca, New YorkPlease send me ........ alblms of Bird Songs, Volume

$10.50 each and ........ albums of Bird Songs Volume I

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Name

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Red-eyed TowheeStarlingWhistling Swan

November 30, 1951

PHOTOVOLTLine-Operated ElectronicMU LTI PLIER-PHOTOM ETER

Mod. 520-M

For the exact measurementof extremely low light valuesdown to 1/10,000 microlumen.

Write for Bulletin #360 to

PHOTOVOLT CORP.95 Madison Ave. New York 16, N. Y.

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7

I I I s pI

1the Bausch & Lomb FL STUDENT MICROSCOPE

gives you these EXCLUS!VETEACHING ADVANTAGES

N Balanced light on full fieldNew Opti-lume integral illuminator lights the entire fieldevenly. Instantly removable for use as separate light source.Ventilated, assuring cool specimen. Standard 15-w., 115-v.clear lamp.

Instantaneous focus ...Saves time, insures accuracy. Pre-focusing gagespeedily sets microscope in accurate focus for slide, regard-less of slide thickness. Saves hours of valuable class time.Eliminates confusion and frustration of prolonged searchingby beginners.

Clearer, sharper, truer imagesSuperb quality 1oX and 43X parfocal B&Lobjectives afford better resolution, flatter fields,for finest image quality. Achromatically cor-rected. Color-coded for quick, sure selection.

SEE FOR YOURSELF INDEMONSTRATION the many exclusivefeatures that make the "FL" the finest studentmicroscope ever offered.

_E~~IT14OT ILCFORA DEMONSTRATION AND LITERATURE TO BAUSCH & LOMR

- - ^l ^ L ~~OPTICAL CO., 642-17 ST. PAUL ST., ROCHESTER 2, NEW YORK

SCIENCE, Vol. 114