DR. PRINCE S AIR-PUMP. 237 



denfing fyringe to it, in the following manner. Let a ftraight ^^^ made to 

 pipe be fixed to the cifterns, and pafs horizontally to the y^- meinsa^I 

 ceiver-plate, as in the common table air-pump. At a con- fyrJngc 

 venient diftance from the barrels this pipe muft be fwelied out 

 fo as to admit the key of a ftop-cock. The key of this cock Stop cock for 

 muft be pierced quite through in the diredion of its handle ; g^^gj^^g^^j^** 

 and halfway through, at a right angle to meet the other hole. 

 A fmall pin muft be fixed in the handle, on that fide which 

 correfponds with the fliort hole. A hole muft be made in the 

 fide of the pipe to correfpond occafionally wl(h the holes in 

 the key. This cock is more fimple than the one in the 

 original pump, and will regulate the exhaufting and conden- 

 fing experiments. To fet the cock for exhaufting the receiver, 

 bring the handle of the key parallel with the pipe, with the 

 folid part of the key againft the hole in the fide of the pipe; 

 then will the communication be opened between the barrels 

 and receiver, and the receiver may be exhaufted. To reftore 

 the equilibrium, or let the air into the receiver, fet tlie handle 

 of the key at right angles with the pipe, and let its projeding 

 pin point to the receiver; then will the communication be 

 opened between the atmofphere and receiver, through the 

 hole in the fide of the pipe and the cock. In this fituation 

 the folid part of the key will clofe the paftagein the pipe lead- 

 ing to the barrels. If a condenfer, having a valve at its end, Mode of con- 

 be now attached to the fide of the pipe, oppofite the hole, the ^^"W* 

 air may be forced into the receiver through the cock without 

 entering the barrels. The fwelied part of the pipe, in which 

 the key is inferted, (hould be fo made as that the condenfer 

 may be fcrewed on or ofl^, at pleafure. The equilibrium may 

 be reftored in the receiver, either by unfcrewing the con- 

 denfer a little, or by letting the air out through the barrels. 



' In this conftru6tion, the pipe ftanding between the barrels The pump thus 

 in the original pump, and the drilled paffages in the horizon- Jj^^'^j^^'^ "'°''* 

 tal piece connecting this pipe with the regulattng cock, are 

 unneceflary. The pump is rendered more firaple, and every 

 diflkulty of execution on account of crooked paffages, &c. 

 removed. Tliis alteration in the American air-pump was con- 

 trived by its inventor, and a table-pump made on this plan, 

 for him, by the late Mr. G. Adams before the laft edition of 

 -ihe Encyclopedia was printed, 



' Another 



