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 



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



Philosophical Society of Glasgow, 

 May 1855, entitled "Outlines of 

 the Science of Energetics," and re- 

 printed in 'Miscellaneous Papers,' 

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



formation of energy (' Lehre von 

 der Energie,' 1887, p. 63). That 

 such a general rule can in the 

 present state of our knowledge 

 be established on purely energetic 



above definition p. 228. James principles is upheld by some (Ost- 



Thomson's contribution is to be wald, Helm) and disputed by 



found in a paper on " Crystalliza- | others (see especially Planck, 



tion and Liquefaction," read before ' ' Thermodynamik,' 1897, p. 7i 



the Royal Society, December 5, 

 1861, in which he establishes and 

 gives examples of the application 

 of "a general physico-mechanical 

 principle or axiom," which indi- 

 cates when a " substance or system 



will pass into the changed state." , later on. 

 As Helm says, it is a first attempt 



sqq.), who state their conviction 

 that the " energy-principle clearly 

 does not suffice for the definition 

 of natural processes." The whole 

 discussion merges into a philos- 

 ophical question, of which more 



