22 INDUCTION. 



what cause may have produced the effect, in order that 

 we may know in what direction to look out for evi- 

 dence to determine whether it actually did. The vor- 

 tices of Descartes would have been a perfectly legiti- 

 mate hypothesis, if it had been possible, by any mode 

 of exploration which we could entertain the hope of 

 ever possessing, to bring the question, whether such 

 vortices exist or not, within the reach of our observing 

 faculties. The hypothesis was vicious, simply because 

 it could not lead to any course of investigation capable 

 of converting it from an hypothesis into a proved fact. 

 The prevailing hypothesis of a luminiferous ether I 

 cannot but consider, with M. Comte, to be tainted 

 with the same vice. It can never be brought to the 

 test of observation, because the ether is supposed 

 wanting in all the properties by means of which our 

 senses take cognisance of external phenomena. It 

 can neither be seen, heard, smelt, tasted, nor touched. 

 The possibility of deducing from its supposed laws a 

 considerable number of the phenomena of light, is the 

 sole evidence of its existence that we have ever to 

 hope for ; and this evidence cannot be of the smallest 

 value, because we cannot have, in the case of such an 

 hypothesis, the assurance 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 con- 

 dition often fulfilled equally well by two conflicting 

 hypotheses ; and if we give ourselves the license of 

 inventing the causes themselves as well as their laws, 

 a person of fertile imagination might devise a hundred 

 modes of accounting for any given fact, while there 



