20 INDUCTION. 



ether witb the resisting medium would even, I imagine, give 

 rise to new ones. At present, however, this supposition cannot 

 be looked upon as more than a conjecture ; the existence of 

 the ether still rests on the possibility of deducing from its 

 assumed laws a considerable number of the phenomena of 

 light ; and this evidence I cannot regard as conclusive, because 

 we cannot have, in the case of such an hypothesis, the assu- 

 rance that if the hypothesis be false it must lead to results at 

 variance with the true facts. 



Accordingly, most thinkers of any degree of sobriety allow, 

 that an hypothesis of this kind is not to be received as probably 

 true because it accounts for all the known phenomena ; since 

 this is a condition sometimes fulfilled tolerably well by two con- 

 flicting hypotheses ; while there are probably a thousand more 

 which are equally possible, but which, for want of anything 

 analogous in our experience, our minds are unfitted to con- 

 ceive. But it seems to be thought that an hypothesis of the 

 sort in question is entitled to a more favourable reception, if, 

 besides accounting for all the facts previously known, it has 

 led to the anticipation and prediction of others which experi- 

 ence afterwards verified ; as the undulatory theory of light led 

 to the prediction, subsequently realized by experiment, that 

 two luminous rays might meet each other in such a manner as 

 to produce darkness. Such predictions and their fulfilment 

 are, indeed, well calculated to impress the uninformed, whose 

 faith in science rests solely on similar coincidences between its 

 prophecies and what comes to pass. But it is strange that any 

 considerable stress should be laid upon such a coincidence by 

 persons of scientific attainments. If the laws of the propaga- 

 tion of light accord with those of the vibrations of an elastic 

 fluid in as many respects as is necessary to make the hypo- 

 thesis afford a correct expression of all or most of the pheno- 

 mena known at the time, it is nothing strange that they should 

 accord with each other in one respect more. Though twenty 

 such coincidences should occur, they would not prove the 

 reality of the undulatory ether ; it would not follow that the 

 phenomena of light were results of the laws of elastic fluids, but 



