582 PHILOSOPHICAL THOUGHT. 



been replaced by that of mass or inertia. And lastly, 

 the terra cause has not escaped a similar process of 

 remodelling, both so far as efficient and final causes 

 are concerned. The school represented by Prof. 

 Mach inclines in the direction of abandoning, for 

 scientific purposes, the special term cause, putting in 

 its place merely antecedence and sequence in time ; 

 Prof. Wundt inclines in the direction of doing 

 away with the conception of substance ; and Prof. 

 Ostwald opposes the conception of matter and sub- 

 stance in favour of the conception of energy, agreeing to 

 some extent with but further elaborating the position 

 already taken up by Tait in this country. Yet most 

 of these thinkers have not refrained from constructing 

 a philosophy of nature upon one or several of the older 

 or more recent terms which are employed in purely 

 scientific reasoning. Thus we have, inter alia, the 

 modern cosmological theory of the gradual and ultimate 

 equalisation of temperature in the universe, and the 

 extinction of the phenomena of life ; * a theory built up 

 by Helmholtz, upon Lord Kelvin's conception of the 

 degradation of energy and the irreversibility of all nat- 

 ural, as distinguished from purely mechanical, processes. 

 We have Prof. Ostwald's recent " Philosophy of Nature," 

 built up exclusively on the conception of energy, 

 discarding the conception of matter and substance as 

 leading to materialism, but introducing the conception 

 of development in the form of the second law of thermo- 



1 It may be well to remark here 

 that the discovery of radium by 

 M. and Mme. Curie in 1898, and 

 the remarkable phenomena of radio- 



activity, may very considerably 

 change our ideas as to the sources 

 of heat and the gradual cooling of 

 the sun. 



