254 DEVELOPMENT AND PURPOSE CHAP. 



the undulatory theory. Nevertheless, logicians like Mill 

 protested from the outset that such coincidence amounted 

 to no proof, and in point of fact, the undulatory theory 

 has given place to a conception of transformations of 

 energy in a medium, the alleged properties of which still 

 present extraordinary difficulties. Professor Ostwald, how- 

 ever, appears to be justified in maintaining that the later 

 tendency is to remove the hypothetical elements and to 

 pare down the theory to a point at which it c approximates 

 to a correlation of the actual facts destitute of hypothetical 

 elements.' We may believe that the electro-magnetic 

 theory of light has still a long path to tread before this 

 result will be consummated, but Professor Ostwald has well 

 stated the general course of development for theories of 

 the kind. So far as they give rise to new experiments they 

 serve a purpose, but while experience expands, the theory 

 itself is narrowed until the two meet, and what was a hypo- 

 thetical account of underlying reality and as such, doubt- 

 ful and pregnant with fallacy becomes a descriptive 

 generalisation of the phenomena of the laboratory or 

 of the field, embodied in a series of mathematical 

 equations. 



The law of Gravitation, again, is constantly taken as a 

 perfect example of the success of the hypothetical method. 

 Yet Newton himself said, ' hypotheses non fingo,' and his 

 critics have not been sufficiently careful to examine what 

 he meant by this disclaimer. Newton, of course, used 

 hypothesis in the sense that he tried the result of calculating 

 from certain suggested forces, that when the result did not 

 appear to tally with experience, he dismissed it, and that 

 when improved methods of observation showed that it did 

 tally with experience, he accepted it, and regarded his 

 theory as proved. But what exactly was proved? Not 

 the nature of gravitation as to this Newton had no hypo- 

 thesis but the conformity of the earth and planets to the 

 modes of motion discernible in the behaviour of bodies on 

 the earth's surface. The ultimate cause of this action was 

 not only not demonstrated by Newton, but is in fact still 

 to seek. Newton's so-called hypothesis is an extension or 

 generalisation of the motions of bodies from the terrestrial 



