116 SCIENTIFIC THOUGHT. 



tion secured on which a new generation could enter 

 at once into the possession of eorrecter dynamical and 

 physical views. It is now being recognised more and 

 more that the word " force " applies only to a mathe- 

 matical abstraction, whereas the word " energy " or 

 " power to perform work " applies to a real quantity ; 

 and there are not wanting suggestions that the former 

 should be altogether banished from scientific text-books, 

 and that the latter denotes not merely a property of 

 matter, but that it is after matter the only real thing 

 or substance in the material world. 1 



This radical change in the fundamental notions which 

 underlie all physical reasoning was not brought about, 

 however, till the vaguer views expounded by Mayer in 

 Germany, and the exact measurements of Joule in England, 

 had been united by the independent labours of Thomson 

 and Clausius, whose earliest researches (also carried on 

 independently of each other) had been suggested by the 



1 The late Prof. P. G. Tait has methods and systems which in- 



on various occasions expressed [ volve the idea of force, there is the 



himself in this sense. See his leaven of artificiality. The true 



lecture on "Force," delivered be- foundations of the subject, based 



fore the British Association. Glas- entirely on experiments of the 



gow, in 1876, and reprinted in : most extensive kind, are to be 



'Recent Advances,' 3rd ed., also | found in the inertia of matter, and 

 the closing paragraphs of his article 

 "Mechanics," in the 9th ed. of the 

 ' Ency. Brit.,' reprinted as ' Dy- 



the conservation and transfor- 

 mation of energy. With the help 

 of kineruatical ideas, it is easy to 



namics,' 1895, where he says (p. j base the whole science of dynamics 



356) : " The only other known 

 thing in the physical universe, 

 which is conserved in the same 

 sense as matter is conserved, is 

 energy. Hence we naturally con- 



on these principles ; and there is 

 no necessity for the introduction of 

 the word ' force,' nor of the sense- 

 suggested ideas oh which it was 

 originally based." We must, how- 



sider energy as the other objective j ever, in that case extend the con- 

 reality in the physical universe, ; ception of matter to embrace also 

 and look to it for information as to the ether (see Tait, ' Properties of 

 the true nature of what we call Matter,' p. 5, 2nd ed.) 

 force;" and (p. 361): "In all 



