290 INDUCTION. 



attempt on the subject of distinctions of sound ; which nevertheless 

 have been found to be immediately preceded and caused by distin- 

 guishable varieties in the vibrations of elastic bodies : although a sound, 

 no doubt, is quite as different as a color is from any motion of particles, 

 vibratory or otherwise. We might add, that, in the case of colors, 

 there are strong positive indications that they are not ultimate proper- 

 ties of the different kinds of substances, but depend upon conditions 

 capable of being superinduced upon all substances ; since there is no 

 ' substance which cannot, according to the kind of light throvra upon it, 

 be made to assume any color we think fit ; and since almost every 

 change in the mode of aggregation of the particles of the same sub- 

 stgince, is attended with alterations in its color, and in its optical prop- 

 erties generally. 



The real defect in the attempts which have been made to account 

 for colors by the vibrations of a fluid, is not that the attempt itself is 

 unphilosophical, but that the existence of the fluid, and the fact of its • 

 vibratory motion, are not proved ; but are assumed, on no other ground 

 than the facihty they are supposed to aflbrd of explaining the pheiiom-- 

 ,ena. And these considerations lead us to the important question of 

 the proper use of scientific hypotheses ; a subject the connexion of 

 which with that of the explanation of the phenomena of nature, and of 

 the necessary limits to that explanation, needs not be pointed out. 



§ 4. An hypothesis is any supposition which we make (either with- 

 out actual evidence, or upon evidence avowedly insuflScient), in order 

 to endeavor to deduce from it conclusions in accordance with facts 

 which are known to .be real; under the idea that if the conclusions 

 to which the hypothesis leads are known truths, the hypothesis itself 

 either must be, or at least is likely to be, true. If the hypothesis relates 

 to the cause, or mode of production of -a phenomenon, it will serve, if 

 adrtiitted,. to explain such facts as are found cf^able of being deduced ' 

 from it; And this explanation is the purpose of many, if not most 

 hypotheses. Since explaining in the scientific sense means resolving 

 an uniformity which is not- a law of cavisation, into the laws of causa- 

 tion from which it results, or a complex law of causation into simpl'er 

 and more general ones from which it is capable of being deductively 

 inferred ; if there do not exist any known laws which fulfill this re(]uire- 

 ment, we may feign or imagine some which would fulfill it ; and this is 

 making an hypothesis. i 



An hypothesis being a mere supposition, there are no other limits 

 to hypotheses than those of- the human imagination; we may, if we 

 please, imagine, by way of accounting for an effect, some cause of a 

 kind utterly unknown, and acting according ta a law altogether fic- 

 titious. But as hypotheses of this sort would not , have any of the 

 plausibility belonging to those which ally themselves by analogy with 

 known laws of nature, and besides would not supply the want which 

 arbitrary hypotheses are generally invented to satisfy, by enabling the 

 • imagination to represent to itself an obscure phenomenon in a familiar 

 light ; there is probably no hypothesis in the history of science in which 

 both the agent itself and the law of its operation were fictitious. Either 

 the phenomenon assigned as the cause is real, but the law accol-ding to 

 which it acts merely supposed ; or the cause is 'fictitious, but is sup- 

 posed to produce its effects according to laws similar to those of some 



