PHYSICAL SCIENCE IN THE NINETEENTH CENTURY 349 



There is in nature a certain magnitude of unsubstantial quality, 

 which keeps its value under all alterations of the objects observed, 

 while its manner of appearance changes most variously. Mayer. 



I shall lose no time in repeating and extending these experi- 

 ments, being satisfied that the grand agents of nature are, by the 

 Creator's fiat, indestructible; and that whatever mechanical force is 

 expended, an exact equivalent of heat is always obtained. Joule. 



Heat and work are equivalent. The entropy of the universe tends 

 to a maximum. Clausius. 



The later eighteenth and the whole of the nineteenth 

 centuries are characterized by increasingly rapid development of 

 the physical sciences, which become more and more completely 

 differentiated, and more and more important in their influence 

 upon industry and civilization. While it is evidently impossible 

 within our available space to describe all phases of this varied 

 development, we shall attempt to enumerate some of those which 

 are most general in their character and most far-reaching in their 

 consequences. A relatively complete and highly instructive 

 review of the whole subject may be found in Merz's History 

 of European Thought in the Nineteenth Century. 



At the beginning of this century mathematics was in a stage of 

 triumphant expansion, in which the related sciences of astronomy 

 and mechanics participated. General physics and chemistry 

 were still in the preliminary stage of collecting and coordinating 

 data, with attempts at quantitative interpretation, while in their 

 train the natural sciences were following somewhat haltingly. 



The most notable advance in physical science during the century 

 is the gradual working out of the great fundamental principle of 

 the conservation of energy, affecting profoundly the whole range 

 of phenomena. Of equal or even greater importance is 

 the gradual realization of progressive development evolution 

 not only in plant and animal life but even in the inorganic world. 

 Physics is gradually enriched by experimental researches and 

 by the working out of mathematical theories of heat, light, 

 magnetism and electricity. Chemistry, largely hitherto a collec- 

 tion of unrelated facts, becomes more and more coordinated with 



