THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 131 



The concept of molecule as used to explain physical and 

 chemical phenomena appears to be in possession of all these 

 marks. The data are the modes of behaviour of molar bodies 

 which cannot be regarded as homogeneous with the modes of 

 behaviour of the individual molecules of which the former are 

 assumed to exhibit only the statistical result.* Secondly, if 

 physicists' calculations of the "size" of molecules and their 

 conclusions as to the " wave-length of light " are both to be 

 accepted, molecules must in all probability be un verifiable. t 

 Finally, in this case it is one of the expressed " objects of 

 Physical Science to explain natural phenomena by means of 

 the properties of matter in motion," J where by " explain " is 

 probably meant to exhibit the reality of which the phenomena 

 in question are only the appearances. 



64. 



On the question of the validity of these various types of hypo- 

 theses our own doctrine is clear. The first and second classes 

 consist of hypotheses which suggest definite interpolations where 

 interpolations are demanded by our previous experiences. The 

 " other context " from which an hypothesis of this type is drawn 

 consists of experiences of the same class as those which the 

 hypothesis ideally completes. This completion, as such, is the 

 sole object of such hypotheses, which, when verified, become 

 merged in the Objective facts which they have served to make 

 intelligible. None of these things can be said of hypotheses of 

 the third class. They are interpolated where there is little or 

 nothing to warrant interpolation. They are drawn from 



* Cf. in particular "Ward, Naturalism and Agnosticism, i, pp. 92-111. 



t I leave it to the competent to decide whether this does not make 

 the assumption of their existence self -contradictory. 



| J. J . Thomson, Applications of Dynamics to Chemistry and Physics, 

 p. 15. 



Personal opinions will always differ as to the amount of such 

 warrant in particular cases e.g., in interposition of an " ether " to explain 

 action at a distance." Cf. Larmor, B.A. Report, 1900, p, 627. 



K 2 



