128 THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 



on behind what we see and feel " over the whole surface of the 

 Objective, it became inevitable that individuals should take 

 up a definite general attitude towards them, only to be aban- 

 doned exceptionally : that is, that they should adopt a more 

 or less explicit philosophy of Science. For those who accepted 

 the claims of the new concepts, " atoms," " energy," " ether," 



and the like became metaphvsical terms, the names of ultimate 



. 



realities, or of an hierarchy of realities, of which what we have 

 described as the Objective is only the appearance. As meta- 

 physical entities it was inevitable that they should eventually 

 claim to be able to account for the whole of experience. Thus 

 was developed that " mechanical philosophy " which has recently 

 suffered such a severe cross-examination by the author of 

 Naturalism and Agnosticism. 



60. 



We may, it would seeni, distinguish usefully between three 

 distinct types of " secondary construction " to all of which the 

 name hypothesis has been indifferently given. In the first 

 kind the data are a number of facts of experience which 

 form an incomplete spatio-temporal system of a familiar type. 

 The hypothesis here simply suggests additional elements of the 

 same order that would make the system complete. A detective's 

 hypothesis of a crime is of this kind. It interpolates between 

 the data or "clues " other spatio-temporal facts of the same order 

 as the clues, which with the latter would make a system which 

 from its conformity with our experience would be felt to be com- 

 plete. The hypothesis that the collection of fossil bones labelled 

 Diplodocus Carnegii in the Natural History Museum once formed 

 the skeleton of an enormous living reptile, is another example 

 of the same kind of hypothesis. It is evident that the spatio- 

 temporal links which such an hypothesis introduces between 

 the data are always of such a character that they might 

 at least conceivably have been verified. Thus some museum 

 on the surface of Mars might conceivably contain, besides a 



