HYPOTHESES. 23 



had not, a few pages before, taken pains to refute it,* by main- 

 taining that even the exploded scientific hypotheses might 

 always, or almost always, have been so modified as to make 

 them correct representations of the phenomena. The hypo- 

 thesis of vortices, he tells us, was, by successive modifications, 

 brought to coincide in its results with the Newtonian theory 

 and with the facts. The vortices did not indeed explain all 

 the phenomena which the Newtonian theory was ultimately 

 found to account for, such as the precession of the equinoxes ; 

 but this phenomenon was not, at the time, in the contemplation 

 of either party, as one of the facts to be accounted for. 

 All the facts which they did contemplate, we may believe on 

 Dr. Whewell's authority to have accorded as accurately with 

 the Cartesian hypothesis, in its finally improved state, as with 

 Newton's. 



But it is not, I conceive, a valid reason for accepting any 

 given hypothesis, that we are unable to imagine any other 

 which will account for the facts. There is no necessity for 

 supposing that the true explanation must be one which, with 

 only our present experience, we could imagine. Among the 

 natural agents with which we are acquainted, the vibrations 

 of an elastic fluid may be the only one whose laws bear a 

 close resemblance to those of light ; but we cannot tell that 

 there does not exist an unknown cause, other than an elastic 

 ether diffused through space, yet producing effects identical 

 in some respects with those which would result from the un- 

 dulations of such an ether. To assume that no such cause 

 can exist, appears to me an extreme case of assumption with- 

 out evidence. 



I do not mean to condemn those who employ themselves 

 in working out into detail this sort of hypotheses ; it is useful 

 to ascertain what are the known phenomena, to the laws of 

 which those of the subject of inquiry bear the greatest, or 

 even a great analogy, since this may suggest (as in the case 

 of the luminiferous ether it actually did) experiments to 

 determine whether the analogy which goes so far does not 



* P. 251 and the whole of Appendix G. 



