Preface 



problems, the problem of life. They circum- 

 scribe it little by little, reducing certain pheno- 

 mena to physico-chemical laws. Science gains 

 progressively upon mystery; it is not forbidden 

 to hope that the day will come when the great 

 enigma will be deciphered in its turn. But no 

 science has formed a closer alliance with physics 

 than chemistry. They have the same object, 

 principles and methods, and it is impossible to 

 say where the one finishes and the other begins. 

 Merged one in the other they collaborate in a 

 common task. 



Thus physics has been the^mainspring of 

 the other sciences, has imposed upon them its 

 laws, its methods and its experimental pro- 

 cedure. Nowadays every well-constructed ex- 

 periment is necessarily a physical experiment. 

 It is in this way that the unity of science is 

 made and that is the chain which links the 

 sciences together. It is useful to recognise the 

 fact, not only in order to comprehend the 

 evolution which is so characteristic of our epoch, 

 but also to solve a difficulty which results from 

 this evolution. 



Step by step with the creation of unity in 



xiii 



