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in tline, according to tlie fevcral views and addrefs of the 

 makers. 



In our further account of the air-pump,, we (hull trace 

 the various aherations it has undergone from the rude and 

 inconvenient conllruftion ot Otto de Giicricke to its pre- 

 fect improved ftate. Guericke's uiachine is exhibited in 

 P. '.!!<: iv, Ptifumatics, Jig. 24. It eonfills of an iron tlu'ee« 

 l'-''.;'a;ed frame, a b c d f, fuppoiting a round iron plate, h c, 

 in the middle of which is inlerted a hrafs fyringe, _;■ h. The 

 upper part of this fyringe is furniflicd with a rim of lead,_y, 

 (Jig. A.) ; and it is faftened below by means of an iron ring, 

 i i, and three iron arms, 000, to the legs of the frame. 

 Within the rim y, there is a brafs plate m n, (_/%'. B.) en- 

 compalfed by a ring of leather, and fixed by three ferews 

 which tern-.inates upwards in a fmall tube n, into which the 

 pipe connetted with the vetl'el to be exhaulled is inferted, 

 as occafion requires, and to which, on the lower fide, is 

 adapted a valve of leather, through which the air paifes 

 into the fyringe. In this plate there is alfo another fmall 

 valve at z, opening upwards, through which it efcapes. 

 This plate is covered by a copper veffel, x x, intended for 

 containing water. The pillon of the fyringe s /j, {Jig. 24, 

 and Jig. C.) is conncftcd by a joint at /, with the iron rod 

 / ti, which is failencd to the handle, tv u u ; and this moves 

 ri/und the pin at to, by which it is connefted with one of 

 the legs of the frame. In order to prevent air from en- 

 tering into the fyringe, a copper veifel of water is fnfpendcd 

 by hooks to the arms, 0, 0, 0, io that the lower part of the 

 fyringe at i i, and the pillon, may be always covered with 

 water, when the niachine is at work. The receiver, L, is 

 a glafs fphere, adapted to a brafs cap, P P, which has a 

 pipe with a Ilop-cock, ij r ; and this pipe is fitted to the 

 tube, n, above mentioned. From this brief defcrlption of 

 the machine, its operation will be eafily undcrdoud. When 

 the pifton, s h, is depreffed, the air will be expanded in 

 the fyringe, g h, and that of the receiver will defcend into 

 it through the valve in the lower furface of the plate, m n ; but 

 when the pifton is elevated, and the air is compreffed, this 

 valve (hutting upwards will clofe the paffage to the receiver, 

 and make its cfcape through the valve z, which opens up- 

 wards. In order to render the exhauftion more complete, 

 a fmall exhaufting fyringe is adapted to the plate, which is 

 reprefented at tn. See Guericke's Exper. Nov. Magdeb. 

 Amil. 1672. lib.iii. c. iv. and v. p. 77. 



This machine, though it might be deemed an excellent 

 contrivance at the time of its invention, when the doftrine 

 of the elallicity and expanfion of the air was new, had 

 many defeats which it is hardly neceffai-y now to mention. 

 The force necelfary for working it was very great, and the 

 progrefs of its operation veiy flow. Befides, it was to be 

 wrought under water, and it allowed of little change of 

 fubjefts for experiments. Mr. Boyle, whofe ideas of this 

 machine, firft fuggefted to him by Schottus's report of 

 Guericke's conilruclion, were executed by Dr. Hooke, 

 whom he then employed as his operator, removed fome of 

 thefe inconveniences and diminiftied others. 



The form of Mr. Boyle's air-pump appears in Plate iv. 

 Pneumatics, Jig. 25. It confifted of a fpherical receiver. A, 

 with a round hole at the top, whofe diameter, B C, was 

 about four inches ; this was covered with a plate, having a 

 brafs rim, D E, which was firmly cemented to the ring of 

 glafs that furrounded the hole ; and to the tapering orifice 

 of the brafs rim was adapted a brafs hopple, F G, ground 

 fo exactly as to exclude as much as polfible the admihion of 

 air. In the centre of the cover was a hole, H I, of about 

 half an inch in diameter, provided with a focket, to which 



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the brafs ftopplc, K, was fo fitted as to prevent the entrance 

 of air ; and the lower part gf this llopple was perforated 

 with a hole, through which paficd the llrlng, 8, y, 10, for 

 the convenience of moving to and fro the mbjcfts of expe- 

 riments. To the neck of the receiver a Hop-cock, N, was 

 failened ; and to the ihank of the cock, X, a tin-plate, 

 MTU W, was fo cemented as to preclude the adminiun of 

 air. The lower part of this machine confilled of a wooden 

 frame with tluee legs, ill, and a tranfverfc board, 222, 

 on which the pump relied. The cylinder of this pump was 

 caft brafs ; and it was fitted with a fucker, 4 4, 5 5 ; of 

 which one part, 44, was covered with (hoe-lealhet, fo as 

 cxailly to fill the cavity of the cylinder ; and to this was 

 faftened the other part, which was a thick and narrow plate 

 of iron, 5 j, fomewhat longer than the cylinder, indented 

 on one edge with narrow teeth, io as to admit the coiTef- 

 ponding teeth of a fmall iron nut, faftened by two ftaples 

 to the under fide of the tranfverfe board 2, 2, 2, on which 

 the cylinder refts ; and this is turned to and fro by the 

 handle, 7. The la ft part of this cylinder is the valve, R, con- 

 fifting of a hole bored through at the top of the cylinder, 

 fomewhat tapering towards the cavity ; into which hole is 

 ground a tapering, peg of brafs, to be thrull in and taken 

 out at pleafure. In order to prevent more efiedlually the 

 adniiffion of air, and to prepare the fucker of the pump for 

 motion, a quantity of fallad oil was poured in at the top of 

 the receiver and alfo into the cylinder. The operator, having 

 fixed the lower fliank, O, of the ftop-cock into the upper 

 • orifice of the cylinder, turns the handle, and thus foixes the 

 fucker to the top of it, fo that no air may be left in its 

 upper part. Then fliutting the valve with the plug, and 

 turning the handle the other way, he draws down the fucker 

 to the bottom of the cylinder, and thus its cavity, into 

 which no air is admitted, wiU be in an exhaufted ilate. By- 

 turning the ftop-cock, and opening a paflage between the 

 cylinder and the receiver, the air contained in the one will 

 defcend into the other ; and this air being prevented from 

 returning, by turning back the key of the Ilop-cock, will 

 be made to open the valve and to efcape into the external 

 air by forcing the fucker to the top of the cyhnder ; by al- 

 ternately moving the fucker upward and downward, turning 

 the key and flopping the valve, as occafion requires, the ex- 

 hauftion may be continued. See Boyle's Works, by Bircli, 

 vol. i. p. 7 — 10. 



Mr. Boyle has defcribed a fecond air-pump in the firft con- 

 tinuation of his Phyfico-mechanical experiments. See his- 

 works, vol. iii. p. 180. This, like the former, had only- 

 one barrel, by which the receiver was exhaufted ; bat it was 

 fo contrived as to be every where furrounded with water, 

 that the ingrefs of air might be more eftei'luallv prevented. 

 Befides, the receivers, which were of feveral forms and 

 fizes, were faftened to an iron plate by means of a foft 

 cement, fo tiiat they coidd be removed and changed at 

 pleafure. The interpofition of a moiftened leather for fixing 

 them, does not feem at this time to have occuired to him. 



Notwithilanding all the precautions of Mr. Boyle, and 

 his contrivances for excluding air by oil and leather, he 

 found that the working of his pump by a fingle barrel was 

 laborious, on account of the preft'ure of the atmofphere, a 

 great part of which was to be removed at evei-y elevation of 

 the pifton, when the exhauftion was nearly completed : 

 and he himfelf candidly acknowledges, that it was rarely 

 and with great difficulty, that he was able to produce any- 

 great degree of rarefaftion. This ufefid macliine was gra- 

 dually improved by Papin, Merfenne, Mariotte, and others ; 

 but the introduftion of a fetond bai'rel and pifton was the 



principal 



