432 MR W. J. M. RANKINE ON THE CENTRIFUGAL THEORY OF ELASTICITY, 
Hence, temperature depends on the above function only ; for the definition of 
temperature is, that bodies at the same temperature are in a permanent condition 
as to heat, so far as their mutual action is concerned. 
The ratio of the veal specific heat of (a) to that of (?) is obviously 
hk, + hy iy le he Ml te a ai oat AM bic 
(7.) Measure of Temperature and Specific Heat—The function @ is proportional 
to the pressure of a perfect gas at a constant density. That pressure, therefore, 
is the most convenient measure of temperature. 
Let 7+ denote absolute temperature, as measured by the pressure of a perfect 
gas at constant density, and reckoned from a certain absolute zero, 274-6 Centi- 
grade, or 494°-28 Fahrenheit below the temperature of melting ice. Let « be a 
constant which depends on the length of a degree on the thermometric scale, and 
is the same for all substances in nature. 
Then 
T=Kk O= ae +K : ; é ; ; 2 é 
(15.) 
hk 
Q=(7=*) 5 SEARS RES hE te TST | 
and the real specific heat of the substance, that is to say, the depth of fall, under 
the influence of gravity, which is equivalent to arise of one degree of temperature 
in the body, is represented by 
hk 

The pressure of a perfect gas is represented in terms of temperature by 
hut 
p= ay Syed Rat a. te 
It may also be expressed thus: let 7, denote the absolute temperature of melt- 
ing ice in degrees of the scale employed, and V, the volume of unity of weight of 
the substance in the theoretical state of perfect gas, at the temperature of melting 
ice and pressure unity :—then 
Gace 
pe Ee i eRe Ot ALD 61 SANE AS OEE (18.) 
On comparing this with equation (17) we see that 
AS Ni 
ONE Pear ; . | 
pa tT, he LK a 


—MV,’> MV, 7, 
Now 4 is the specific elasticity of the atomic atmosphere of the substance ; a 4 
0 
is the mean specific gravity of that atmosphere, when the body is in the theoretical 
state of perfect gas; and « andr, are the same for all substances in nature. There- 

