HYPOTHESES. 21 



at most that they are governed by laws partially identical with 

 these ; which, we may observe, is already certain, from the fact 

 that the hypothesis in question could be for a moment tenable.* 

 Cases may be cited, even in our imperfect acquaintance with 

 nature, where agencies that we have good reason to consider 

 as radically distinct, produce their effects, or some of their 

 effects, according 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 coincidence of results pre- 

 dicted from an hypothesis, with facts afterwards observed, 

 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 inscription. 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."f If 

 any one, from examining the greater part of a long inscrip- 

 tion, can interpret the characters so that the inscription gives 

 a rational meaning in a known language, there is a strong 

 presumption that his interpretation is correct; but I do not 

 think the presumption much increased by his being able to 

 guess the few remaining letters without seeing them : for we 

 should naturally expect (when the nature of the case excludes 



* What has most contributed to accredit the hypothesis of a physical 

 medium for the conveyance of light, is the cei'tain fact that light travels, (which 

 cannot be proved of gravitation,) that its communication is not instantaneous, 

 but requires time, and that it is intercepted (which gravitation is not) by inter- 

 vening objects. These are analogies between its phenomena and those of the 

 mechanical motion of a solid or fluid substance. But we are not entitled to 

 assume that mechanical motion is the only power in nature capable of exhibiting 

 those attributes. 



t Phil, of Disc. p. 274. 



