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SCIENTIFIC THOUGHT. 



tion secured on which a new generation could enter 

 at once into the possession of correcter 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 

 on various occasions expressed 

 himself in this sense. See his 

 lecture on "Force," delivered be- 

 fore the British Association. Glas- 

 gow, in 1876, and reprinted in 

 'Recent Advances,' 3rd ed., also 

 the closing paragraphs of his article 

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

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

 namics,' 1895, where he says (p. 

 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- 

 sider energy as the other objective 

 reality in the physical universe, 

 and look to it for information as to 

 the true nature of what we call 

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



methods and systems which in- 

 volve the idea of force, there is the 

 leaven of artificiality. The true 

 foundations of the subject, based 

 entirely on experiments of the 

 most extensive kind, are to be 

 found in the inertia of matter, and 

 the conservation and transfor- 

 mation of energy. With the help 

 of kinematical ideas, it is easy to 

 base the whole science of dynamics 

 on these principles ; and there is 

 no necessity for the introduction of 

 the word ' force,' nor of the sense- 

 suggested ideas on which it was 

 originally based." We must, how- 

 ever, in that case extend the con- 

 ception of matter to embrace also 

 the ether (see Tait, ' Properties of 

 Matter,' p. 5, 2nd ed.) 



