HYPOTHESES. 355 



§ 6. It is perfectly consistent with the spirit of the method, to assume in 

 this provisional manner not only an hypothesis respecting the law of what 

 we already know to be the cause, but an hypothesis respecting the cause 

 itself. It is allowable, useful, and often even necessary, to begin by asking 

 ourselves what cause may have produced the effect, in order that we may 

 know in what direction to look out for evidence to determine whether it 

 actually did. The vortices of Descartes would have been a perfectly legit- 

 imate hypothesis, if it had been possible, by any mode of exploration which 

 we could entertain the hope of ever possessing, to bring the reality of the 

 vortices, as a fact in nature, conclusively to the test of observation. The 

 vice of the hypothesis was that it could not lead to any course of inves- 

 tigation capable of converting it from an hypothesis into a proved fact. 

 It might chance to be c^wproved, either by some want of correspondence 

 with the phenomena it purported to explain, or (as actually happened) by 

 some extraneous fact. " The free passage of comets through the spaces in 

 which these vortices should have been, convinced men that these vortices 

 did not exist."* But the hypothesis would have been false, though no such 

 direct evidence of its falsity had been procurable. Direct evidence of its 

 truth there could not be. 



The prevailing hypothesis of a luminiferous ether, in other respects not 

 without analogy to that of Descartes, is not in its own nature entirely cut 

 off from the possibility of direct evidence in its favor. It is well known 

 that the difference between the calculated and the observed times of the 

 periodical return of Encke's comet, has led to a conjecture that a medium 

 capable of opposing resistance to motion is diffused through space. If 

 this surmise should be confirmed, in the course of ages, by the gradual ac- 

 cumulation of a similar variance in the case of the other bodies of the solar 

 system, the luminiferous ether would have made a considerable advance 

 toward the character of a vera causa, since the existence would have been 

 ascertained of a great cosmical agent, possessing some of the attributes 

 which the hypothesis assumes ; though there would still remain many dif- 

 ficulties, and the identification of the ether with the resisting medium 

 would even, I imagine, give rise to new ones. At present, however, this 



mental faculties and propensities, was, on the part of its original author, a legitimate example 

 of a scientific hypothesis ; and we ought not, therefore, to blame him for the extremely slight 

 grounds on which lie often proceeded, in an operation which could only be tentative, though we 

 may regret that materials barely sufficient for a first rude hypothesis should have been hastily 

 worked up into the vain semblance of a science. If there be really a connection between the 

 scale of mental endowments and the various degrees of complication in the cerebral system, the 

 nature of that connection was in no other way so likely to be brought to light as by framing, 

 in the first instance, an hypothesis similar to that of Gall. But the verification of any such 

 hypothesis is attended, from the peculiar nature of the phenomena, with difficulties which 

 phrenologists have not shown themselves even competent to appreciate, much less to overcome. 



Mr. Darwin's remarkable speculation on the Origin of Species is another unimpeachable 

 example of a legitimate hypothesis. What he terms "natural selection" is not only a vera 

 caum, but one proved to be capable of producing eff'ects of the same kind with those which 

 the hypothesis ascribes to it ; the question of possibility is entirely one of degree. It is un- 

 reasonable to accuse Mr. Danvin (as has been done) of violating the rules of Induction. The 

 rules of Induction are concerned with the conditions of Proof. Mr. Darwin has never pre- 

 tended that his doctrine was proved. He was not bound by the rules of Induction, but by 

 those of Hypothesis. And these last have seldom been more completely fulfilled. He has 

 opened a path of inquiry full of promise, the results of which none can foresee. And is it 

 not a wonderful feat of scientific knowledge and ingenuity to have rendered so bold a sugges- 

 tion, which the first impulse of every one was to reject at once, admissible and discussible, 

 even as a conjecture ? 



♦ Whewell's PAiV. o/'Ascorery, pp. 275, 276. 



