Via Kew ConJliiiBloiis of the Air-Pump, 



fliould infalliWy open at the requifite periods of the operation, and that the fpace betweeh 

 the pillon and the apper or tlie lower valve, when at its extreme pofitions, {houUI be the 

 lead polTible, or rather that there (hould be no vacuity remaining. It has been fliown that 

 in the air-pump of Prince the lower fpace is abfolutcly out of the quedion, becaufe there i» 

 no lower valve ; and the upper fpace may be, and probably is, much diminifhed by the effect 

 of the oil. The air-pump of Cuthbertfon, in which the con(lru£lion of the valves is mod 

 admirable, and their atlion abfolutely fecured, feems to poflefs a (lill greater portion of this 

 laft advantage from the circulation of the oil, though not direftly intended to aiifwer this 

 purpofe. Mr. Sadler has direded his attention immediately to the good effeds which a 

 due application of that fluid is calculated to produce, and has conllruQcd an air-pump, pof- 

 fcdnig the defirable requifites of fimplicity, cheapnefs and power, of which Figure I. 

 Plate XIX. is a Iketch. 



A B reprefents the barrel, Q^a folid plfton or plunger fitted into the barrel, and leathered 

 fomewhat loofely. O is the pillon-rod, capable of being raifed and dcprefled in the ufual way 

 by a handle and toothed wheel which aflsupon tlie {Iraight rack-work. The barrel commu- 

 nicates, by means of the pipe C, with a chamber D, at the upper part of which is a valve K, 

 opening upwards into aciftern L. P is the plate for the receiver, through which a commu- 

 nication-pipe N E pafl'es to the interior part of the velTel, D. At the lower extremity E of 

 this pipe there- is a valve, conncded with the lever F H, by a wire F t pafling through a 

 collar of leathers. G is the axis of the lever FH, upon which, by means of a weight at 

 H an aftion is produced which pretTcs the valve E upwards into its place. H I is another 

 wire or tail, by means of which the extremity H of the lever may be raifed, and confe- 

 quently tlie valve E opened. 



From thefe particulars the effeifl of the machine may be explained. Let the pifton bs 

 drawn out and the barrel filled with oil, which will of courfe rife to the fame level in D. 

 Let the pifton then be put in and prefled downwards by turning the handle. The oil will 

 be driven from the barrel into D, driving the air before it through the valve K fo com- 

 pletely, that a portion of the oil itfelf will follow into the ciftern L. Let the pifton be 

 again drawn upwards, and the oil will follow, becaufe D is higher than the vaWe, and 

 will confequently leave an empty fpace in this veflel D. As foon as the pifton-rod has ar- 

 rived at a certain height, it will a£l by means of a prominence upon the catch I, and 

 open the valve E. A portion of the air in the receiver will therefore rufti into D. Upon 

 the return of the pifton the valve E will in the firft place fhut, and the air in D will be ex- 

 truded through K. This extrufion will be as complete as before, becaufe at every ftroke a 

 portion of oil from the ciftern L will pafs through the pipe L M to the upper part of the 

 barrel, and efcape befidc the piflon while rifing, on account of the loofe manner in which it 

 is leathered. From this contrivance it is provided that the internal part of the machine 

 fhall contain oil fufficient not only to difplace the air, but even to pafs through in a fm.dl 

 quantity after it by means of the valve K ; and confequently, by working the apparatus the 

 cxhauftion may be carried to any deCred degree. Fig. 2. reprefents the fame machine 

 viewed in another dire£tion. 



In the prefent pump the valve K may he confidered as rcprefenting the valve which clofes 

 the upper part of the barrel in Cuthbertfon's pump, and the valve E as tlie lower fixed valve. 

 Wc fee therefore from this combination that the folid pifton is made to a^ both ways, in 



the 



