HYPOTHESES. 



329 



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 coinci- 

 dence by persons of scientific attain- 

 ments. If the laws of the propagation 

 of light accord with those of the vibra- 

 tions of an elastic fluid in as many 

 respects as is necessary to make the 

 hypothesis afford a correct expression 

 of all or most of the phenomena 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 fol- 

 low that the phenomena of light were 

 results of the laws of elastic fluids, 

 but at most that they are governed 

 by laws partially identical with these ; 

 which, we may observe, is already 

 certain, from the fact that the hypo- 

 thesis in question could be for a 

 moment tenable.* Cases may be 

 cited, even in our imperfect acquain- 

 tance with nature, where agencies 

 that we have good reason to consider 

 as radically distinct produce their 

 effects, or some of their effects, accord- 

 ing to laws which are identical. The 

 law, for example, of the inverse square 

 of the distance, is the measure of the 

 intensity not only of gravitation, but 

 (it is believed) of illumination, and of 

 heat diffused from a centre. Yet no 

 one looks upon this identity as proving 

 similarity in the mechanism by which 

 the three kinds of phenomena are 

 produced. 



According to Dr. Whewell, the co- 



* What has most contributed to accredit 

 the hypothesis of a physical medium for 

 the conveyance of light, is the certain fact 

 that light travels, (which cannot be prored 

 of gravitation ;) that its communication is 

 not instantaneous, but requires time ; and 

 that it is intercepted (which gravitation 

 is not) by intervening objects. These are 

 analogies between its phenomena and those 

 of the mechanical motion of a solid or fluid 

 substance. But we are not entitled t» 

 assume that mechanical motion is the only 

 power in nature capable of exhibiting those 

 attributes. 



incidence of results predicted from an 

 hypothesis with facts afterwards ob- 

 served amounts to a conclusive proof 

 of the truth of the theory. "If I 

 copy a long series of letters, of which 

 the last half-dozen are concealed, and 

 if I guess these aright, as is found to 

 be the case when they are afterwards 

 uncovered, this must be because I 

 have made out the import of the in- 

 scription. To say, that because I 

 have copied all that I could see, it is 

 nothing strange that I should guess 

 those which I cannot see, would be 

 absurd, without supposing such a 

 ground for guessing."* If any one, 

 from examining the greater part of 

 a long inscription, can interpret the 

 characters so that the inscription 

 gives a rational meaning in a known 

 language, there is a strong presump- 

 tion that his interpretation is correct ; 

 but I do not think the presumption 

 much increased by his being able to 

 guess the few remaining letters with- 

 out seeing them : for we should 

 naturally expect (when the nature of 

 the case excludes chance) that even 

 an erroneous interpretation which 

 accorded with all the visible parts of 

 the inscription would accord also with 

 the small remainder ; as would be the 

 case, for example, if the inscription 

 had been designedly so contrived as 

 to admit of a double sense. I assume 

 that the uncovered characters afford 

 an amount of coincidence too great to 

 be merely casual : otherwise the illus- 

 tration is not a fair one. No one sup- 

 poses the agreement of the phenomena 

 of light with the theory of undulations 

 to be merely fortuitous. It must arise 

 from the actual identity of some of 

 the laws of undulations with some 

 of those of light ; and if there be that 

 identity, it is reasonable to suppose 

 that its consequences would not end 

 with the phenomena which first sug- 

 gested the identification, nor be even 

 confined to such phenomena as were 

 known at the time. But it does not 

 follow, because some of the lawa agree 



* Phil, of Disc, p. 274. 



