1888 - 89 .] Prof. Tait on Virial Equation for Molecular Forces. 71 
measure of temperature accounts for the so-called latent heat of 
vapours. And it is clear that similar reasoning may he extended to 
the passage from the liquid to the solid state. A great number of 
very curious results follow as immediate consequences of this mode 
of regarding the temperature of a group of particles, but this is not 
the place for them. 
If, -with Van der Waals and Clausius, I had taken the whole 
kinetic energy as the measure of the absolute temperature, my 
equation would have been of the form 
which does not seem fitted to represent Andrews’ results. 
For the reasons given above, I think we ought to write 
p(Y + 
This may be made to resemble closely Van der Waals’ equation if 
we take /? = (Aa - Cy)/(A - C) ; but I see no physical reason for 
this assumption. 
It is clear, from the point of view which I have taken, that the 
equation as given cannot be more than a rough approximation to 
the truth. The calculation of the proper values of the constants, 
to adapt it with great accuracy to Andrews’ results for carbonic acid, 
would involve considerable labour : — more perhaps than the results 
to be obtained are worth. 
I have therefore, guided by the indications given above as to the 
relative magnitudes of a, /?, y, tentatively found values of the con- 
stants, which (while eminently simple for calculation) are on the 
face of them obviously provisional, but which sufficiently show how 
well-fitted the formula is to express the main facts. The resulting 
equation which I first got in this way is 
^(V-2) = 1000 2 -^^ 
5000 2000 
V -4 + V - 5 ’ 
where p is in atmospheres, and T is temperature Centigrade. The 
carbonic acid has volume 1000 at 0° C. and 1 atm. 
This formula gives three equal values of Y (7*8), for a pressure 
of 91 atm., and temperature about_35°*5 C. These are only in rough 
