82 THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 



But a study of this valuable and interesting address shows 

 'that Professor Divers' real concern is to propound and illus- 

 trate a doctrine of the functions of the atomic hypothesis fjiul 

 hypothesis which is identical with that defended in this essay. 

 For him, as for us, the starting point of the science of chemistry 

 is a definite series of Objective facts. " The facts of a chemical 

 nature about common salt which cause the statement to be 

 made that it is a chemical compound of chlorine and sodium 

 are such as these : Salt can be wholly changed into sodium 

 and chlorine ; these substances brought together change into 

 salt and nothing else ; salt and sodium, each under conditions 

 appropriate to it, change into the same substance, called also 

 a sodium compound, such as sodium hydroxide: salt and 

 chlorine, each in its OWB way, change into the same chlorine 

 compound, such as hydrochloric acid ; neither sodium nor 

 chlorine, one apart from the other or the other's chemical 

 compounds, ever changes into salt . . . ." Some such 

 ''primary facts" as these, presenting themselves in ,a few 

 instances to Kobert Boyle, were apperceived, that is, were 

 rendered intelligible to him by the concept of undissolved 

 "primary concretions" of ultimate hard particles of different 

 kinds existing side by side in the "grosser corpuscles," and 

 recoverable therefrom without change. This concept, as we 

 saw, led to the formulation of a definite problem the problem 

 of determining in the case of a given substance what other 

 substances can "combine" to form it: or, as Professor Divers 

 (following Professor Duhem in his " return to Aristotle "*) 

 has taught us to say, what substances "change" into it and 

 under what conditions. Quite similarly, the really important 

 result from .a critical point of view of the renewed application 

 v by Dalton of theaatomic concept to chemical facts, is that it has 

 led to the definite fqrmulation of a further question. This is 

 the problem of determining what weights of substances display 



* Duhem, Le Mixte et la Combinaison chimique, Ch. I. 



