Stoney—Of the Kinetic Theory of Gras. 363 
heats (at constant pressure and at constant volume) has the follow- 
ing value— 
ss | 2 
oe ay 
where m is the number of terms—each the square of a momentoid 
multiplied by a selected co-efficient—in the expression for the 
energy. Now observation gives y in many cases, and we thus 
arrive, by the foregoing equation, at m, the number of the terms 
in the expression of 7, which is the same as the number of 
degrees of freedom in the molecule of those events with which the 
theorem is concerned, if the constitution of the gas be such that 
the theorem approximately applies to it. ‘To what motions these 
degrees of freedom are to be supposed to correspond will depend 
on what experiment has been made use of in determining y. If 
the experiment is one that lasts a long time—for instance a whole 
second or more—then almost the only motions that are concerned 
are the A and the Bw motions; but if it depends on rapidly 
changing events, as where the velocity of sound in the gas is the 
fact that is ascertained, then we may expect that some of the Bod 
events will also influence the result. It is very convenient to 
distinguish the internal events into Ba motions and Bb motions ; 
but it must be remembered that this distinction is one of degree, 
and that, although in most gases they appear as different as is 
the chin from the cheek, it would nevertheless be quite as impos- 
sible to indicate precisely where the one ends and the other 
begins. 
The following Table of the best determinations of y is given 
by Mr. Capstick in Science Progress for June, 1895. I have 
added the last two columns in which are given the values of m 
which the determinations would suggest, if the Boltzmann- 
Maxwell Theorem could be regarded as holding good for the 
gas :— 
[Taste oF CasEs. 
2D2 
