ON THE PHYSICAL VIEW OF NATURE. 



167 



The train of thought methodically and comprehen- 44. 



Willard 



sively followed out in Gibbs's various memoirs had its Gibbs - 

 origin in the early speculations of William Thomson 

 (Lord Kelvin) and Clausius, to which I referred above. 

 Thomson was the first who, in adopting (after much 

 hesitation) the mechanical view of the phenomena of heat, 

 the doctrine of the convertibility and equivalence of the 

 different forms of energy, recognised that, in order to 

 describe natural phenomena correctly, this view required 

 a qualification. The change of the different forms of 

 energy into each other can for the most part take place 

 only in one direction; there is a general tendency in 

 nature towards a degradation or dissipation of energy. 

 Energy, though not lost, becomes less useful, less avail- 

 able. The least available form of energy is heat; and 

 it is in that form that in all natural changes a por- 

 tion of energy becomes lost, dissipated, or hidden away. 

 Thus we have to recognise the difference between 

 available and unavailable, between useful and useless, 

 energy. In the sequel Thomson showed in definite 

 instances l how to calculate the available and the un- 



1 See ' Math, and Phys. Papers,' 

 vol. .i. No. LIX., 1852, " On a Uni- 

 versal Tendency in Nature to the 

 Dissipation of Mechanical Energy"; 

 and No. LXIII., 1853, "On the 

 Restoration of Mechanical Energy 

 from an unequally heated Space." 

 In Tait's ' Sketch of Thermodynam- 

 ics' (1868), we read (p. 100): "It 

 is very desirable to have a word to 

 express the availability for work of 

 the heat in a given magazine, a 

 term for that possession the waste 

 of which is called Dissipation. Un- 

 fortunately the excellent word en- 

 tropy, which Clausius has introduced 



in this connection, is applied by him 

 to the negative of the idea we most 

 naturally wish to express. It would 

 only confuse the student if we were 

 to endeavour to invent another 

 term for our purpose." He then 

 proceeds to use the term entropy 

 in an altered sense, in which it 

 measures the available instead of 

 the unavailable energy, creating 

 for some time a great confusion 

 and some unnecessary irritation. 

 See on this the early editions of 

 Clerk Maxwell's excellent ' Theory 

 of Heat,' and the footnote to p. 

 189, 8th ed., and Clausius 'Die 



