Prof. P. Gr. Tait on the Dissipation of Energy. 345 



" contains it. But the extreme practical value is only 



t 

 " where t is the temperature of the body, and to the lowest 

 " available temperature. This value may be written in the 

 " form 



J&q-Jt^. 



" Hence, in any cyclical process whatever, if q 1 be the whole 

 " heat taken in, and q that given out, the practical value is 



%-go)-JUj' 



J* 



" Now the realized value is 



" by the first law ; and if the cycle be reversible, this must be 

 u equal to the extreme practical value. Hence, in this parti- 

 " cular case, 



" But in general this integral has a finite negative value, 

 " because in non-reversible cycles the realized value of the heat 

 " is always less than 



" which is the extreme practical value. 



" Hence the amount of heat lost needlessly, i. e. rejected in 

 " excess of what is necessarily rejected to the refrigerator for 

 producing work, is 



t 



" This is Thomson's expression for the amount of heat dissipated 

 " during the cycle (Phil. Mag. and Proc. E. S. E. 1852, < On a 

 " Universal Tendency in Nature to Dissipation of Energy '). 

 " It is, of course, an immediate consequence of his important 

 " formula for the work of a perfect engine. 



" [It is very desirable to have a word to express the availa- 

 " bility for work of the heat in a given magazine ; a term for 

 " that possession, the waste of which is called dissipation.]" 



As I based the greater part of the last chapter of my work 



* On this formula Prof. Clausius remarks, " Die Unrichtigkeit dieses 

 11 Resultates lasst sich leicht aus dem blossen Anblicke der Fomiel 

 "erkennen"! 



-J- 



