ON THE PHYSICAL VIEW OF NATURE. 



139 



The exposition of Helmholtz, however, does not seem to 

 have been understood or accepted. The general recog- 

 nition of the relation of active and latent forces dates 

 rather from Thomson's and Rankine's writings in 1851 

 and the following years. Thomson uses the term 

 " mechanical energy " (later, from 1851, intrinsic 

 energy, or simply energy), and considers this quantity 

 to be a measure of the store of power to do work 

 which a material system possesses ; 1 and Rankine, 2 

 early in 1853, introduces and defines the terms actual 

 (or sensible) energy and potential (or latent) energy, 

 which are at once adopted by Thomson 3 in the place 

 of the terms dynamical and statical energy, which he 



29. 



"Poten- 

 tial " and 

 "actual" 

 energy. 



1 The memoir of Thomson in 

 which he introduces the physical 

 conception of the quantity "energy " 

 in the place of a merely mathema- 

 tical symbol used by Clausius, and 

 inaugurates the terminology of 

 modern physics, is contained in 

 the ' Transactions of the Royal 

 Society of Edinburgh,' vol. xx., 

 Part 3 (read December 15, 1851, 

 and reprinted in ' Math, and Phys. 

 Papers,' vol. i. p. 222), as an ap- 

 pendix to the great paper " On the 

 Dynamical Theory of Heat, with 

 Numerical Results deduced from 

 Mr Joule's Equivalent of a Thermal 

 Unit, and M. Regnault's Observa- 

 tions on Steam " (Trans. Edinb. 

 Soc., March 1851 : reprinted in 

 ' Phil. Mag.,' 1852, and ' Math, 

 and Phys. Papers,' vol. i. p. 174 

 tqq. ; see especially p. 186, note). 

 The term energy had indeed been 

 used by Thomson already in 1849 

 as a synonym for mechanical effect, 

 but he had not then accepted 

 the dynamical theory. He merely 

 puts the question in a footnote to 

 his exposition of Carnot's theory : 

 " When thermal agency is ... 



spent, what becomes of the 

 mechanical effect which it might 

 produce ? Nothing can be lost in 

 the operations of nature no energy 

 can be destroyed " (' Papers,' vol. i. 

 p. 118, 1849). 



2 In a paper read before the 

 Philosophical Society of Glasgow, 

 January 5, 1853, reprinted in 

 ' Miscellaneous Scientific Papers, ' 

 ed. Millar, p. 203 sqq. See also 

 Rankine's note, dated 1864, in the 

 28th vol. of the 4th series of the 

 ' Phil. Mag.,' p. 404. 



3 See the Proceedings of the 

 Glasgow Philos. Soc., January 

 1853, reprinted with additions 

 from Nichol's 'Cyclopaedia' (1860) 

 in 'Math, and Phys. Papers,' vol. 

 i. p. 521. In this paper Thomson 

 also introduces the term " electrical 

 capacity " of a conductor. Thom- 

 son subsequently introduced the 

 word " kinetic " in place of " actual " 

 energy. See also Thomson's Lec- 

 ture before the Royal Institution, 

 February 29, 1856, reprinted in 

 ' Math, and Phys. Papers,' vol. ii. p. 

 182, and 'Popular Lectures,' vol. 

 ii. p. 418, especially the note to p. 



