292 Mr. P. G. Tait on the History oj Thermo -dynamics. 



holtz's "Erhaltung" is an identical word, and was employed 

 before Rankine wrote on the subject. But the term Energy (as 

 Dr. Tyndall surely is aware) is due to Young, who introduced it 

 as a convenient English term synonymous with vis viva. Its exten- 

 sion to the two forms " static" and "dynamic" was made by 

 Thomson. Rankine improved these to "potential" and "actual;" 

 and in l Good Words ' Thomson and I have employed " kinetic " 

 as less ambiguous and more suggestive than " actual." 



As to the discovery of the Conservation of Energy, I hold that 

 to lay down, without experimental bases, such a maxim as " causa 

 cequat effectum " is entirely subversive of common sense and logic 

 in an experimental science such as natural philosophy. The esta- 

 blishment of the Conservation of Energy was utterly out of the 

 sphere of the "Thinker;" and it would be absurd to give him 

 more credit than is due to the promulgator of a clever specula- 

 tion. Thousands of equally clever, but less lucky, though not 

 more baseless, speculations are every day mercilessly extermi- 

 nated by experiment. 



Celestial Dynamics forms no part of the Thermo- dynamic 

 theory, though it affords exceedingly beautiful applications of it. 

 The same must be said of Animal and Vegetable Physiology. 

 Such applications, as is well illustrated by the famous little sen- 

 tence of JomVs postscript of 1843, always attend careful work 

 at a theory ; they are not discoveries, but inevitable consequences, 

 to the experimental or mathematical investigator. The word or 

 two, required to complete the suggestions of Stephenson and 

 Herschell, occurred to many minds, merely to be recorded in 

 passing — as by Helmholtz in a popular lecture, and by Thomson 

 in the proceedings of a society. 



I have written again to the Philosophical Magazine because I 

 imagine that Dr. Tyndall still misunderstands the views which 

 Prof. Thomson and I maintain on the history of the subject; 

 and that it is this which has led him to charge us with misrepre- 

 sentations. His special charges against Prof. Thomson, which 

 receive fresh development in every successive article, are so ob- 

 viously unfounded that he can hardly be surprised that Prof. 

 Thomson has not judged it necessary even to notice them. 



I am, Gentlemen, 



&c. &c, 



P. Guthrie Tait. 



6 Greenhill Gardens, Edinburgh, 

 September 12, 1864. 



