116 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.^ 



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 



^ The late Prof. P. G. Tait has methods and systems which ia- 

 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, ba.sed 

 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 the conservation and transfor- 

 " Mechanics," in the 9th ed. of the , mation of energy. With the help 

 'Ency. Brit.,' reprinted as ' Dy- of kinematical ideas, it is easy to 

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

 356) : " The only other known I on these principles ; and there is 

 thing in the physical univer.se, ; no necessity for the introduction of 

 which is conserved in the same j the word ' force,' nor of the sense- 

 sense as matter is conserved, is j suggested ideas on which it was 

 energy. Hence we naturally con- ' originally based." We must, how- 

 sider energy as the other objective ever, in that ca.se 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 



