F K Cipher— The Isentropic Cu 



> the slope of ar 

 the surface, dz 

 the v,T plane, we have 



dz *Jdv* 

 ch by (5) becomes 



nd by (6) we have further 



In determining the din 

 it is evident that A and 3 

 required condition, 



Substituting the values of A and ] 



For very low pressures, the direction of maximum slope — - 

 becomes more and more nearly at right angles to the plane of 

 p,v; while for high pressures this direction becomes more and 

 more nearly parallel to the plane of p, v. The direction of 

 maximum slope is constant along a line of constant pressure. 



2°. To find the direction of the isentropic line at any point 

 on the surface, as related to the direction of maximum slope 

 determined in (9). 



Poisson's equation : 



TV-^const. (10) 



is a projection of the isentropic line upon the plane of v, T, 

 where k is the ratio of the specific heats = 141. 



Calling a' the tangent of the angle which any element of this 

 projection makes with the v axis, we have 



is obtained by differentiating (10) and 



