170 SCIENTIFIC THOUGHT. 



the universal tendency in nature towards a dissipation 

 of energy, by saying, " The entropy of the world is 

 always on the increase." 



For about twenty years after these conceptions had 

 been introduced into scientific language and reasoning, 

 mathematicians and physicists were mainly occupied 

 in defining more clearly this hidden quantity, and in 

 defending what was called the second law of thermo- 

 dynamics against misconceptions and attacks. In 1875 

 Lord Eayleigh could still say, 1 "The second law of thermo- 

 dynamics and the theory of dissipation founded upon it 

 has been for some years a favourite subject with mathe- 

 matical physicists, but has not hitherto received full 

 recognition from engineers and chemists, nor from the 

 scientific public. And yet the question under what 

 circumstances it is possible to obtain work from heat 

 is of the first importance. Merely to know that when 

 work is done by means of heat, a so-called equivalent of 

 heat disappears, is a very small part of what it concerns 

 us to recognise." 



Whilst these words correctly describe the general 



attitude of the scientific public towards this important 



discovery, two men had already made a beginning in 



Horstmann. the direction indicated Horstmann 2 in Germany, and 



1 ' Proceedings of the Royal In- 

 stitution,' vol. vii. p. 386. 



2 Prof. Ostwald in the historical 

 section of his ' Verwandtschafts- 

 lehre ' ('Allg. Chemie,' 2nd ed., 

 vol. ii. part 2, p. Ill, &c.), Helm 

 in 'Energetik' (p. 141, &c.), and 

 Duhem in his ' Traite" de Mecanique 

 chimique' (1897, vol. i. p. 84, &c.) 

 all do full justice to the long-un- 

 recognised labours of Horstmann, 



which began in the year 1869 and 

 were continued in Liebig's 'An- 

 nalen ' in various communications 

 during the early 'seventies, not 

 without undergoing violent attacks 

 from representatives of the older 

 conceptions. Ever since James 

 Thomson's celebrated prediction 

 (see above, p. 126), physicists 

 had recognised the importance of 

 thermo - dynamical considerations, 



