Condensation 6? Rarefaction of Air, 513EXPERIMENT 4.

Inclosed a wine glass with .about a cubic inchof water in it, containing the bulb of a thermo-ineter, in a receiver; and, exhausting the air,thethermometer sunk half a degree suddenly, gndthen continued stationary; upon restoring theair it suddenly rose half a degree.

All these experiments confirmed my. .conjec-ture of a much greater degree of heat and coldbeing produced in these cases than the thermo-meter points out, but that its continuance is soshort as not to effect a material change in thetemperature of the mercury. The followingexperiments were made to ascertain what may bethe real degree of heat and cold generated inthose operations.

, EXPERIMENT 5 .

The same receiver & small thermometer as abovebeing used, I found the exhaustio.n was effect-ed by working the pump one minute. The ther-mometer sunk nearly 2° in the first half minute,and the remainder, a few tenths of a degree, inthe latter half minute. The operation beingstopped, and things remaining in the samestate, it required some minutes of timebefore the thermometer recovered one degreevol. v. c c