Condensation & Rarefaction of Air. 517

degree, I proceeded to ascertain several factsexperimentally.

EXPERIMENT 1.

Took a receiver, the capacity of which wasabout 120 cubic inches, and suspended the ther-mometer with its clear bulb in the central partiof it; then letting the whole acquire the tem-perature of the room, which was without a fire,I exhausted the air and afterwards restored it,marking the effects upon the thermometer. Themedium of several trials nearly agreeing witheach other was as under :

The Thermometer

--in the air of the room stood at-—Z6°.8

■ . sunk upon exhaustion to .34 .7

—-rose when the air was restored 10 -38 .9

The suddenness of the fall and rise puzzled memost : after reflecting upon it for some time,I conjectured that the real change of tempera-ture of the air or medium was much greater thanthe thermometer indicated, but that the ine-quality existed only for a few seconds of time,because the receiver, &c. immediately impartheat to or abstract it from so small a quantityof air as 120 cubic inches, which are only equalto 40 grains in weight,—The phenomena of the