~98 -~Zechanics' Re~ister.

In fine weather there w'as o n the contrary a strong draft down into the well.

Eight months afterwards t h e well was again entered when the strat~m of blue sand and black p e b b l e s appeared tbrmirg into plumb-puddling stone. The welt was rendered sa fe by bricking" it down to the chalk, and applying a thick coating of compost o v e r the whole. Dr. Mitchell explains the phe- nomena by observing t h a t t h e tbul air was no doubt sulphuretted hydrogen, produced by the decomposi t ion of water and iron pyrites. After long-con- tinued rain, water p e n e t r a t i n g into the bed dislodged the gas accumulated in the interstices where it w a s formed; while after dry weather had cot, tinued for some time, the openings produced in this bed on drying up wouhl draw tbr a short time a supply o f air to fill up the vacuities, and hence ti~e draft observed to pass down it~to the well. The whale of the neighbouring dis- trier, to the extent of fou r miles , is called by the well-diggers, fool co~mtry. Similar phenomena w e r e observed in digging a well on the opposite bill at Applebury, and also in t b r m i n g some wells in the immediate vicinity of Lon- don. Ibid.

~ [ e e h a n i c s ~ ] ¢ e g i s t c r .

Plumbago and Bl, ek Lead Pencils. There is only one p u r p o s e to which this form of carbon is applied in the

solid state, viz., for the manufac tu re of black lead Pencils~ and its adaptation to this end depends on its softness. In the state of a powder, plumbago is used to relieve friction. I t s power in this way may be illustrated by rub- bing a button first on a p l a i n board, five or six times, and applying it to a bi tof phosphorus, the l a t t e r will immediately burn. When rubbed one surface covered with p l u m b a g o , double or triple the friction will be required to produce the same e f fec t . One of the most remarkable circumstances connected with plumbago, is the mode in which it is sold. Once a year the mine at Borrowdale is o p e n e d , and a sufficient quantity of plumbago is ex- tracted, to supply the m a r k e t (luring the ensuing year. It is then closed up9 and the product is carr ied in small fragments of about three or four inches long, to London, where it is exposed to sale, at the black lead market~ which is heht on the first M o n d a y of every month, at a public-house, in Es- sex.-street, Strand. T h e buyers , who amount to about seven o r eight~ examine every piece w i t h a sharp instrument, to ascertain its hardness.---. those which are too soft b e i n g rejected. The individual who has the first choice pays 45s. per p o u n d , the others 30s. But as there is no addition made to the first quantity in the market, (luring the course of the year, the residual portions are e x a m i n e d over and over again, until they are exhaus- ted. The annual amoun t o f sale is about 3000/. There are three kinds of pencils, common, ever -poin ted~ and plummets. The latter are compos- ed of one-third sulphuret o f antimony, and two-thirds plumbago. The first part of the process is sawing" out the cedar into long planks, and then into what are technically t e r m e d tops and bottoms. The second, sawing out the grooves by means o f a fly-wheel. The third scraping the lead on a stone, having been p r e v i o u s l y made into thin slices, to suit the groove: introducing it into the g r o o v e , and scratching the side with a sharp-pointed instrument, so as to b r e a k it off exactly above the groove. The tburth, g|ueiug the tops a~ld b o t t o m s together, and turning the cedar cases in a gauge. The ever.pointed pencils are first cut into thin slabs~ then into

Edge 17ails.~ ~teel Letter.press Engravln~'. 299

square pieces, by means of a steel gau~e. They are then passed through three small boles, armed with rabies, which last about three or four days* Steel does not last above as many hours. Six of these ever-pointed pen. cils may be t~ad for 2s. 6d. If they are cheaper than this, we may be sure that they are adulterated. In Paris, w h e n y o a b u y a sheet of paper in a siationer~s shop, some of those pencils are added to the purchase. Now, these are formed of a mixture of plambag% f~ller's earth, and vermicelli. Genuine cedar pencils must cost 6d. each. I f they are sold at a lower price they must be formed from a mixture, not from pure plumbago. Pencils are, however, soht as low as 4~d. a dozen. There is no patent which has been more infringed on than that of Mordan~s~ for ever-pointed pencils. Birming. ham is the source of this infringement, where they are sold as low as~d. each, formed of composition. A thousand persons are now engaged in the manu/'actnre of these pencils and pet;cil-cases. These fitcts were stated by Dr. Faraday, at the Royal lnstitution~ April 22.--etrcana of Science.

1~ in. Jour.

Edge Rails. The edge rail has now entirely superseded the tram or Ira;n-plate, and

is used in all railways worked by locomotive engines. This form of rail causes much less fi'iction to the wheels, there being considerably less sur- face of the tbrmer coming in contact wilh the latter. These rails are made of wroaghtiron, in 15-feet lengths~ with an upper flanch slightly curving from tim middle to the sides; the weight of rail is regulated by the tonnage passing along the line. 0n the Stockton and Darlington, Manchester and Liverpool, and Leeds nnd Selby Railways, the weight per lineal yard o[" the original rails is 35 lbs. On the Manchester Railway9 however, rails of 751bs. are beinffsubstituted. The size of the351b, rail is3~ inches in depth, 2¼ inches as to the width oftl~e upper flanch, and the upright portion three-quarters of an inch thick. The original rails of the London and Birmingham Railway, are 50 Ibs, in ~eight, as also those of the Greenwich Railway; but on the former line 751b. rails are being laid down, to a considerable extent. The Manchester and Bolton rail is 50lb. to the yard, but differs in shape from those used on every other railway. The top flanchis 2] inches wide, the bottom flanch 4~inches wide, the depth 2~6 inches, and the thickness of the middle portion three quarters of an inch.--l~Fhishaw's ,~nalysis of Railways.

Min, Jour .

Steel Letter Pres,~ Engraving. A young artist of Vienna, named yon Sieglander, ha% we are informed

by the German papers, recently discovered a process by which he can ex- ecute engravings in the style e[ copperplate, which can~ nevertheless, be printed with letter-press in the same manner as wood cuts, This invention may prove of some importance. The Hamburgh Correspondent tells us with as much solemnity as it speaks of the invention i that Mr. Ficker, Pro. lessor of Asthetics, at the High School of Vienna, has already given it the name of Chalcox/2/ograph~t. l~e¢.mg.