‘288 
ON THE THERMODYNAMIC THEORY OE WAVES. 
quantity ; being the proposition which is demonstrated in an elementary way near the 
beginning of the present paper. Mr. Eaknshaw regards that condition as one which 
cannot be realized. 
The new results, then, obtained in the present paper may be considered to be the fol- 
lowing : — the conditions as to transformation and transfer of heat which must be fulfilled, 
in order that permanence of type may be realized, exactly or approximately ; the types 
of wave which enable such conditions to be fulfilled, with a given law of the conduction 
of heat ; and the velocity of advance of such waves. 
The method of investigation in the present paper, by the aid of mass-velocity to express 
the speed of advance of a wave, is new, so far as I know ; and it seems to me to have 
great advantages in point of simplicity, enabling results to be demonstrated in a very 
elementary manner, which otherwise would have required comparatively long and elabo- 
rate processes of investigation. 
