is the heat energy thus directly transferred from the hot to the cold body,
the absolute temperature of the hot body and
that of the cold body.
THE WORK OF FRICTION IS CONVERTED INTO HEAT
The group under head (b) contains a class of events which usually attends, in one form or another, most natural phenomena.
We will here consider an interesting (but perhaps too special) case, namely, the experiment performed by W. THOMSON and JOULE on the flow of gas through a porous plug. The plug obstructed the uniform, non-conducting, passage through which the gas was forced without sensibly changing its velocity of flow: (See LORENZ' Technische Wärmelehre, p. 275). It can easily be shown (in L., p. 274) that with an ideally perfect gas,
