in IDEAL GENESIS OF MATTER 255 



universe, nor even that such an affirmation has any 

 meaning ; for the universe is not made, but is being 

 made continually. It is growing, perhaps indefinitely, 

 by the addition of new worlds. 



Let us extend, then, to the whole of our solar 

 system the two most general laws of our science, 

 the principle of conservation of energy and that of its 

 degradation, limiting them, however, to this relatively 

 closed system and to other systems relatively closed. 

 Let us see what will follow. We must remark, first 

 of all, that these two principles have not the same 

 metaphysical scope. The first is a quantitative law, 

 and consequently relative, in part, to our methods of 

 measurement. It says that, in a system presumed to 

 be closed, the total energy, that is to say the sum of its 

 kinetic and potential energy, remains constant. Now, if 

 there were only kinetic energy in the world, or even if 

 there were, besides kinetic energy, only one single kind 

 of potential energy, but no more, the artifice of measure 

 ment would not make the law artificial. The law of 

 the conservation of energy would express indeed that 

 something is preserved in constant quantity. But there 

 are, in fact, energies of various kinds, 1 and the measure 

 ment of each of them has evidently been so chosen as 

 to justify the principle of conservation of energy. Con 

 vention, therefore, plays a large part in this principle, 

 although there is undoubtedly, between the variations 

 of the different energies composing one and the same 

 system, a mutual dependence which is just what has 

 made the extension of the principle possible by measure 

 ments suitably chosen. If, therefore, the philosopher 

 applies this principle to the solar system complete, he 



1 On these differences of quality see the work of Duhem, L Evolution de 

 la m&anique, Paris, 1905, pp. 197 ff. 



