( 381 ) 
& + 1% == Eat Pit 
With the symbol 7=«-+ pv chosen by GIBBS, we may represent 
the process shortly by 
A1 A2 
The vis viva of the progressive motion may be neglected, if 
the velocity of the motion is small. Moreover the section of the 
tube before- and after the tap may be chosen in such a way, that 
the velocity may be considered as invariable. We may therefore 
represent by ¢ the thermodynamic energy of a gas, being in 
equilibrium. 
From the equation: de mane | — p we find, if we assume 
dv /7 Ce, 1 
: RT E 
as equation of state: p= steed 
v—b v 
c=9()—~[s@y—7/ (0). 
The meaning of (7) we find from ¢ = (=) , from which 
follows : 
my a 7) ry 
=P (tf (El 
Vv 
The meaning of p'(T) is therefore the value of the specific heat 
at v=, which we shall represent by ce . If we think the 
substance in a very rarefied state to consist of molecules, which 
do not change with the temperature, we may put ¢ =p (7) = 
7 voo 
constant and sv p(T)== fe. The quantity € is: 
7 : 
e= Pee — SA) TAO). 
Uv 
If we write: 
b 
RES 
v—b v 
the value of 7 becomes as follows: 
