INTRODUCTION 7 



or free energy, as it is called, becomes as small as 

 possible. By this sole principle, Willard Gibbs 

 developed the complete theory of chemical and 

 physical equilibrium ; as Sir Joseph Larmor says, 

 his '* monumental memoir made a clean sweep of 

 the subject ; and workers in the modern experi- 

 mental science of physical chemistry have re- 

 turned to it again and again to find their empirical 

 principles forecasted in the light of pure theory, and 

 to derive fresh inspiration for new departures." 



Simultaneously with the development of ex- 

 perimental research along the several lines we 

 have indicated, there has arisen afresh an interest 

 in and inquiry into the philosophic basis on 

 which is built the whole magnificent structure 

 of modern science. How far is that basis 

 secure ? Are the conceptions of science life- 

 like pictures of any fundamental reality behind 

 the phenomena which alone our senses can 

 apprehend ? Such questions have occupied 

 periodically the ablest minds of certain epochs of 

 history, though in the attempts to find answers 

 no such general consensus of opinion has been 

 reached as we see within the building of science 

 itself. Granted the security of the foundations, 

 the edifice seems designed on a consistent plan, 

 for the relations of its parts present themselves 

 similarly to all minds competent to judge. 



The philosophy of science is intimately con- 

 nected with its history; and interest was stimulated 

 afresh in the philosophical problems involved in 

 physical conceptions by the publication of Mach's 

 great work on the Science and History of 

 Mechanics. To many that book put new life 

 into the subject treated in its pages, and it has 



