THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 71 

 '20. 



I am aware that in view of the vigorous and important 

 attack upon " hypotheses " made by writers of such eminence 

 as Ostwald * my defence of them will appear reactionary. I 

 venture to think, however, that Ostwald fails to distinguish 

 between the real value and the psychological value of hypotheses. 

 Hypotheses, such as Maxwell's displacement, the weight of a 

 molecule, electrons, the carbon-tetrahedron, entropy, heat itself, 

 may not be verifiable and, therefore, have no real value, but 

 their psychological value as " leading us to further investigations 

 of Nature" and prompting to fresh determinations of the 

 Objective may be immense. Ostwald's assertion that scientific 

 advance has taken place in spite of, and not by means of, 

 hypothesis! is, at best, a half truth. It is true that hypotheses 

 have temporarily delayed the progress of Science in some parti- 

 cular field, but when they have disappeared they have generally 

 been devoured by their own children -objective determinations 

 to which they led. To maintain that these determinations 

 would have been made without the hypotheses for example 

 that Maxwell, without the concept of electro-magnetic 

 displacements in the field around a varying current would have 

 thought of locating at points in the field the disembodied 

 relations expressed by his differential equations, the manipula- 

 tion of which led Hertz to discoveries of the highest importance, 

 seems itself to be an indulgence in hypothesis of a thoroughly 

 unwarrantable character. The point of Ostwald's objection to 

 a hypothesis a Bild% used to make the phenomena intelligible 

 is that the Bild will invariably contain elements which are 

 not present in the original observations. There are two answers 

 to this objection. In % the first place it may be urged that this 



* Ostwald, Vorlesungen iiber Naturphilosophie, X, esp. pp. 211-215. 



t Ostwald, op. cit., p. 225. 



J " Dass .... man durch die Benutzung des Bildes in die Darstellung 

 der Erscheinung Bestandtheile hineinbringt, die dem Bilde angehoren, 

 nicht aber der Erscheinung selbst," op. cit., p. 212. 



