142 SCIENTIFIC THOUGHT. 



abstract theory of physical phenomena in general." ^ 

 It is only in our day, after the lapse of a quarter of 

 a century, that these ideas have been taken up by 

 others, and that the plan begins to be realised. The 

 reasons why at the time it was abandoned were 

 manifold. 



To begin with, it was soon found, notably by Joule, 

 Helmholtz, and William Thomson, that the new prin- 

 ciple of the conservation of energy, if applied to various 

 other phenomena outside of the narrower field of ther- 

 motics, led to a co-ordination and comprehension of 

 them which was then quite unexpected : opening out 

 new aspects, disclosing unknown properties, and sug- 

 gesting innumerable experiments. As instances I may 

 refer to the thermo-elastic and thermo-electric pheno- 

 mena of bodies, which very early occupied the atten- 

 tion of the founders of the theory of energy. The 

 discharge of the Leyden-jar, the generation of electric 

 currents in the voltaic cell, the heat of electrolysis, 

 the actions of permanent magnets and those between 



^ In a paper read before the to find a general rule for the trans- 

 Philosophical Society of Glasgow, , formation of energy (' Lehre von 

 May 1855, entitled "Outlines of ] der Energie,' 1887, p. 63). That 

 the Science of Energetics," and re- ] such a general rule can in the 

 printed in 'Miscellaneous Papers,' ; present state of our knowledge 



be established on purely energetic 

 principles is upheld by some (Ost- 

 wald. Helm) and disputed by 



ed. Millar, p. 209 sqq. See for the 



above definition p. 228. James 



Thomson's contribution is to be 



found in a paper on '* Crystalliza- others (see especiallj' Planck, 



tion and Liquefaction," read before " Thermodynamik,' 1897, p. 71 



the Royal Society, December 5, | sqq.), who state their conviction 



1861, in which he establishes and 

 gives examples of the application 

 of "a general physico-mechanical 

 principle or axiom," which indi- 



that the " energj'-principle clearly 

 does not suiBce for the definition 

 of natural processes." The whole 

 discussion merges into a philos- 



cates when a " substance or system i ophical question, of which more 

 will pass into the changed state." later on. 

 As Helm says, it is a first attempt 



