Laws of Irreversible Phenomena. 399 



If, therefore, the general principle is applicable here, the 

 terms in (6) containing 477-01^, &c, should reduce to 



P 1 dt h f 



J to 



Q (10) 



Now the quantity of energy which becomes absorbed from the 

 aether and converted into heat is, for the time dt and the 

 volume \\\dxdy dz, 



-Jjftf.r^(feC(E l rfA l +E/A y + E / /AJ; . (11) 

 hence 



8'Q = Jjj*^ dy dz C (E^A, + E y 8 k y + E z 8 A J :. (12) 



and thus the principle contained in (I.), or in (III.), is again 

 seen to hold good. 



Part II. 



§ 14. Introductory. — The foregoing naturally raises the 

 question, Does a general law exist concerning the infinitesimal 

 expressions d'Q and 8'Q, which have been found to charac- 

 terize dissipation of energy in the various particular cases 

 discussed ? 1 venture to answer this in the affirmative ; 

 but the hypothesis I advance does not profess to be more 

 than a conjecture and an approximation. 



Let us consider in every particular case the quantity 



? = - 2Fs ^ (iv.) 



In the case of irreversible Dynamics, § 9, the function F is 

 well known, and has been called by Lord Rayleigh the 

 "Dissipation Function ;" I should suggest that this term 

 be extended to all cases covered by equation (IV.). 



Let us imagine a material (or at any rate partly material) 

 system. Suppose that it is not in equilibrium, and observe, 

 in a quantitative maimer, the disturbances which its state 

 involves. Let it be isolated so as not to be disturbed by ex- 

 traneous action. We know from experience that under such 

 circumstances the disturbances in the system must finally 

 subside and tend to disappear. This general behaviour may 

 be called the coercion of disturbances, because of the contrast 

 it offers with inertia. (See Phil. Mag. for June 1895, p. 509.) 

 For definiteness let us consider a continuous body. Let 

 dxdydzp be the mass of an element dxdydz, and let 

 dxdydzpf represent its dissipation function, so that F, the 

 dissipation function for the portion ^^ dxdydz of the bodv, 



