A I R 



plate which ctofe? the barrel, being foldered into It, (hewing 

 the place of tlic valves over the three fmall holes. /Vf. 5 I, is a 

 peqicndicLilar IcCtion of the button) piece, pipes, valvc-pun-.p, 

 coii, &c. at right angles with the other fei^ion, /i;^. 49. Tlie 

 button is fcreweif here into the top inllead of the gage. 

 C D ii the valve-pump and ciftern, c the place of the valve 

 iimhr the cnp ; K I" the cock, (hewing the duct through it 

 leading to the atniofphere ; G H the pipe leading from it to 

 the fteni of the receiver plate, in which is the cock I, to 

 ihut up the AuA wiion the plate i> \ifed as a transferrer. K 

 K is the plate; I. a piece to fluit up the hole, into which 

 tubes, &e. art occalionally fcrewed to perform experiments 

 without removing the plate. Tlie dotted line at O (liews 

 the place of the ferew which preflcs the plate againll the_ 

 pipe ; P Q^ tiic pipe and common gage Handing in fjont of 

 the pump. fi;;. 52, is a horizontal fettiun of the cock, and 

 pieces containing the duds leading from it to the receiver, 

 the cifterns and the valves on the top of the barrels ; A B 

 the duft, connecting the ciilcrns together ; C D tlie dud 

 leading from the cillerns to the cock ; G H the duc\ leading 

 from tile cock through the pipe A li (fg 51.) to the valves ; 

 1) E the dud through the cock, which occafionally con- 

 neds the two lail mentioned duds with the dud E F, 

 leading from the cock to the receiver ; I the dud in the 

 cock leading to the atmofphere, which, when conneded 

 with tlie dud at D, lets the air into the cillerns and b;u-rcls 

 for condcnfation ; the other dud thnKigh tlie cock at the 

 fame time conncding H and E. This dud alio, when con- 

 neded with E, rcllores the equilibrium in the receiver. K 

 L is part of the dud leading from the citterns to the gage. 

 The dotted circles Ihew the places of the pipe and valve- 

 pump on the piece, and /-the place where the air enters the 

 valve-pump from the dud G H, and is thrawn into the at- 

 mofphere when the pump exhaulls. Fig. 53, (licws tlie 

 under furface of the boxes which contain the collars ot 

 leathers with the crofs piece which connedis them together, 

 having a dud tlirough it, as reprelented by the dotted line, 

 through which the air paffes from the valves into the pipe. 

 This figure is chiefly defigned to Ihew the places in which 

 the valves play, as at I. American Tranfai^tions, vol. i. 

 Bofton, 1785. Nicholfon's Journal, vol. i. p. 1 21-128. 

 Adams's Ledures on Nat. and Exp. Philof. by Jones, vol. i. 

 p. 51-54, p. 153. 



The air-pump of Mr. Cuthbertfon is fo excellent in its 

 ftruduie, and (0 powerful in its effed, that it claims parti- 

 cular notice and deicnjition. A perfpedive view ot it 

 apf>ears in PLte viii. Pneumat'us, Jig. 56- Its two prin- 

 cipal gages are fcrewed into their places ; but tliefe need 

 nbt be ufed together, except in cafes where the utnioft ex- 

 adnefs is required. In common experiments, either of them 

 may be taken away, and a llopfcrew put into its place. 

 When the pear-gage is ufed, a fmall round plate, large 

 enough for the receiver to Itaiid upon, muft firft be fcrewed 

 into a hole at A ; but when this gage is not ufed, this hole 

 mud be clofed with a ilop-fcrevv. When all thefc gages are 

 ufed, and the receiver is cxhaulfed, the ftop-fcrtw B, at the 

 bottom of the pump, mull be unfcrewcd, to admit the air 

 into the rect-ivcr ; biit when the gages are not all ufed, the 

 ftop-frrew at A, or either of tlie other two which are in 

 the place of tlic gages, may be uiifcrewed for this purpofe. 

 In /ig, jy^ C D repix'fent.s one of the barrels of the pump, 

 Fthe collar of leathers, G a hollow cylindrical veflll to con- 

 lain oil ; R Is alio an oil-vefTel, which receives the oil that 

 is driven with the air through the hole a a, when the pillon 

 ■is drawn upwards ; and when this is full, the oil is carried 

 over with the aiv along the tube T, into the oil velTel G ; 

 *c ji a wjre wijich is driven upwards from the liole a a, by 



AIR' 



the patTage of the air : and as foon as this has efcapeJ, falls 

 down again by its own weight, (luits up the hole, and pre- 

 vents any air from returning by that way into the barrel ; 

 at titi are fixed two pieces of brafs, to keep the wire cc in 

 fuch a diredion as may prefcrve the hole air-tight. H is a 

 cylindrical wire, whieli carries the piilon I, and is made 

 hollow to receive a long wire, q y, that opens and clofes the 

 hole L, which forms the communication with the receiver 

 Itanding on the plate ; m is part of a pipe, one end of 

 which is fcrewed into the wire q y, that open;, and fhuts 

 the hole L ; and upon the other end, O, is icrewed a nut, 

 which, ftoppiiig in the InuiUer part of the hole, prevents 

 the wire from being lilted too high. This wire and fcrew 

 are more clearly leen in j'lg. S''^' and ^_f. 62 : they Hide 

 through a collar of leathers, rr. Jig. 58, and_^^f. 61, in the 

 middle piece of the pilton. Figures 60 and 61, are the two 

 main parts which compofc the piilon ; and when the pieces 

 iu Jigures 59 and 67, are added to it, the w hole is repre- 

 lented hy Jig. 58. Fig. 61, is a piece of brafs, turned in a 

 conical form, with a ihoulder or ledge at tlie bottom ; a 

 long female-fcrew is cut into it, about two-thirds of its 

 length ; and the remaining part of the hole, in ivhich there 

 is no fcrew, is about the iame diameter as the fcrew part, 

 except a thin plate at the end, which is of a breadth exadly 

 equal to the thicknefs of q q. That part of the infide of 

 the conical piece of brafs, in which no thread is cut, is filled 

 with oiled leathers with holes in them, through which q j 

 can Aide air-tight ; there is alfo a male-fcrew with a hole in 

 it, which is fitted to q q, and ferves to prefs down the lea- 

 thers r r. In Jig. 60, a a a a is the outiide of the pifton, the 

 infide of which is turned exadly to fit tl\e outfide oijig. 6r ; 

 b h are round leathers, about 60 in number ; rr is a circular 

 plate of brafs, of the fize of the leathers ; and dd is a 

 Icrew, which ferves to prefs them down as tight as is necef^ 

 faiy. The male fcrew, at the end of fig. 59, is made to fit 

 the female fcrew wvjig. 61. ^^J'g- f'2, be pufhed '\\\X.ofg. 61, 

 this \\\1oJig. 60, and _^. 59 Icrewed into the end oi Jig. 61, 

 thcfe will compofe the whole piilon, as reprefentcd by^c'. 58. 

 H, mjig. 57, reprelents the fame part as H m Jig. 58, and. 

 is that to which the rack is fixed. If this, therefore, be 

 drawn upwards, it will make Jig. 61 fhut clofe into fig. 60, 

 and diive out the air above it ; and when it is puihed down- 

 wards, it will open as far as the fhoulders a a, {Jig. 60.) will 

 allow, and fuffer the air to pafs through. A A [Jig. 63.) 

 is the receiver plate ; B B ii; a long fquare piece of glafs, 

 Icrewed t-o the undermoll fide of the plate, through which 

 a hole is drilled, cor.'elponding with that in the centre of 

 the receiver plate, and with the three female fcrews b b s. 



In Older to conceive how the rarefadion of the air ij 

 effeded, fuppofe the piilon to be at the bottom of the bar- 

 rel, and a receiver to lland upon the plate, the infide of the 

 barrel, from the top of the piilon to a, is full of air, and 

 the pifton fluit : when drawn upwards, by the hollow cylin- 

 drieal wire li, it will drive the air before it, through the 

 hole a a, into the oil-vcffel R, and out into, the atmofphere 

 by the tube T. The piilon will then be at the top of the 

 barrel at a, and the wire q q will (land nearly as it is repre- 

 fentcd in the figure, jull railed from the tube !>, and pre- 

 vented rifing higher by means of the nut 0. While the pif- 

 ton is moved upwards, the air will expand in the receiver, 

 and be driven along the bent tube vi, into the infide of the 

 barrel. Thus the barrel w-ill be filled with air, which, as 

 the piilon riles, will be rarefied in proportion as the capa- 

 city of the receiver, pipes, and barrel, is to the capacity of 

 the barrel alone. When the piilon is moved downwards 

 again by H, it will force the conical part, jff. 61, out of 

 the hollo iv part, Jig. 60, as far as the Ihoulders a a ; Jig. 58, 

 I. will 



