Various Methods of cofiflniBlitg Ait- Pumps. 121 



not durable, but foon become leaky. If ever thefe pumps, of which engravings are to be 

 feen in the vi'orks of Mufchenbroek and S'Gravefande, were ufed in England, which I think 

 was not the cafe, they muft have been long fuperfeded by the cheaper and more fimple 

 contrivance of valves formed by tying a ftrip of bladder over a fmall hole through which the 

 air is allowed to pafs in one diredliou only. IVlr. Smeaton was of opinion, that the opera- 

 tion of the air-pump is rendered defedive from the fmall furface of preffure at which the 

 air acts againft the bladder of the lower valve, as well as frona the preflure of the external 

 air, which is fuppofed to prevent the upper valve from opening in the laft ftages of the pro- 

 cefs. To remedy thefe imperfe£lions, he made a number of hexagonal holes inftead of the 

 one fmall hole in the valve ; and by pafling the rod of the pifton through a collar of leathers 

 at the top of the barrel, which was clofed, with the exception of a valve opening outwards, 

 he prevented the external air from afling upon the valve of the pillon in its defcent *. 

 Mr. Abraham Brooke of Norwich, by experiments with the common air-pump, has rendered 

 it at leaft doubtful, whether, in pumps equally well made, thefe be improvements at allf. 

 But, previous to the time this laft author wrote, there exifted two other air-pumps, con- 

 taining improvements both in principle and workmanfliip fuflicient to annihilate any contro- 

 verfy refpe£ling the merits of the common pump, and that of Smeaton. Thefe were made 

 by the Rev. Mr. Prince, of Salem in North America, and Mr. John Cuthbertfon of Amfter- 

 dam. The firft is defcribed in the only volume of Memoirs publilhed by the American 

 Academy, and is fcarcely known in the philofophical world. The other is defcribed in a 

 publication J by the inventor; of which the circulation muft, in the ordinary courfe of 

 things, be conGderably limited. I have thought it my duty to prefent both to the world in 

 this place. 



Mr. Prince's paper contains a confiderable portion of matter relative to the air-pump of 

 Smeaton, partly defcriptive of the improvements made by that ingenious mechanic, and 

 partly by way of comparifon with his own. For the fake of brevity, I have omitted thefe, 

 and other matters of lefs confequence -, but in the eflential parts of the account I have kept 

 as nearly as poffible to the words of the author. 



From the account of Mr. Smeaton's fuccefs in facilitating the opening of the valves at 

 the bottom of the barrel and in the pifton, Mr. Prince fuppofed, if thofe valves were en- 

 tirely removed, and the remaining air in the barrel could be more perfe£lly expelled, the 

 rarefacUon might be carried ftill further. Upon this plan he conftrufted his pump. He 

 removed the lower valve, and opened the bottom of the barrel into a ciftern on which it was 

 placed, and which had a free communication with the receiver. For the valve on the plate 

 at the top of the barrel (which is conftrufted like Smeaton's) makes it unneceflary, as he 

 remarks, that there (hould be any at the bottom in order to rarefy the air in the receiver. 



The ciftern is deep enough to allow the pifton to dcfcend into it below the bottom of the 

 barrel. Suppofc then the pifton to be folid, that is, without a valve in it ; when it enters 

 the barrel and rifes to the top plate, w hich is made .lir-tight with a collar of leathers, &c. 



• Philofophical Tranfaaions, XLVII. 



t Miftcllaneous Expciiments and Remarks on Eltftridiy, f>c. l,y A. Brooke. Norwich, 1789. P. uj, 

 And clfcwlicrc. > 



t Dcfcripiion of an improved Air Pump. By John Cuthhertfon. Ofl<iv«, 41 pages. London; no date. 

 This artill is at prefent fciilcd in London. , . 



Vol.. I.— June 1797. R like 



