-Fog Mr. PRINCE's Account of 
 inferted. ^ By this mean the pump is made more cónvenientand: 
fimple, as the head of it is brought down upon the ‘top of the 
barrels, in the fame manner as.in the common air-pump? ^ "The- 
barrels alío-ftand upon the fame plane with the receiver-plate ;. 
and this plane is raifed high enough toadmit the commonsa oC: 
of thirty-two or three inches, to ftand under it; without any 
| inconvenience in working the pump, as the winch moves thro' 
-a ljó portion of an arch, at each. ftroke,. than-it would if the 
piftons moved the whole:length of thebarrels; °° 50005 
2: There: is.alfo-placed, between. the barrels in«this:pump,-: on 
the erofs-piece over the valves, a gage to:meafure the ‘degree 
of condenfation, having a free communication with ithe valves; 
Cock, &e. This gage is fo: conftrücted, \thatit will alfo ferve 
to. meafure ithe rarefaction above the> valves, when: the air ds 
worked. off by the valvespump. ~ It!confifts ofsa: pedeítal; 
- Which forms a ciftern for the mercury, a hollow brafs- pillar, 
and glaís: tube, hermetically fcaled at one-end,. which: moves. 
up and down.in.the pillar,;throügh a collar of leathers;:; The ` 
dye of the pedeftal is made‘of glafs, as: well to-hold the iquick= 
filver, as to expofe its furfaceto view,; that it may be feen when: 
tthe;open:end of the tube is put down: into it; or raifed out of 
it... /Fhe body of the pillar. is partly cut-away: to expofe the. 
‘If the pump be-ufed as à condenfer; the.degree of condenfa-- 
«tionis fhown by a fcale marked on one edge of the pillar : if it 
- ‘beuufed as an exhaufter, the degree of the rarefaction of the air; 
above the valves, is fhown by a feale marked on the other edge 
“of the pill ürcadi Dior: ae ob enolic adica deis 
Tí hisgage will alfo ferve to fhow' when the valves have done 
‘playing, either with the weight of: the: atmofphere on them, 
Boriy B o C) or 
m 
| AUF? 
