184 
DE. E. P. PERMAN, DR. W. RAMSAY, AND MR. J. ROSE-INNES, 
sively the values 710,000, 720,000, 730,000, 740,000, 750,000, 760,000 ; such a system 
is shown in fig. 5 ; the curves have been drawn for a great part of their length so 
as to exhibit to the eye their general shape, but only that portion of the system which 
is intersected by the drawn isothermals has been really investigated experimentally, 
mid can, therefore, be safely trusted. The adiabatic for h = 720,000 passes close to 
the critical point. 
t'ig. 5. 
The system of isothermals and adiabatics intersecting one another divides the plane of 
pv into a set of curvilinear parallelograms, such as that suggested in Maxwell’s ‘Theory 
of Heat’ (p, 156); and, if our interpretation of the experimental results is correct, 
it ought to be possible so to select the system of adiabatics that the areas of all the 
parallelograms are equal. The following thermo-dynamic investigation will sho\v to 
what extent this can be done. 
