358 INDUCTION. 



sis, 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 elas- 

 tic fluid may be the only one whose laws bear a close resemblance to those 

 of light ; but we can not 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 undula- 

 tions of such an ether. To assume that no such cause can exist, apj^ears to 

 me an extreme case of assumption without evidence. And at the risk of 

 being charged with want of modesty, I can not help expressing astonish- 

 ment that a philosopher of Dr. Whewell's abilities and attainments should 

 have written an elaborate treatise on the philosophy of induction, in which 

 he recognizes absolutely no mode of induction except that of trying hy- 

 pothesis after hypothesis until one is found which fits the phenomena; 

 which one, when found, is to be assumed as true, with no other reservation 

 than that if, on re-examination, it should appear to assume more than is 

 needful for explaining the phenomena, the superfluous part of the assump- 

 tion should be cut off. And this without the slightest distinction between 

 the cases in which it may be known beforehand that two different hypoth- 

 eses can not lead to the same result, and those in which, for aught we can 

 ever know, the range of suppositions, all equally consistent with the phe- 

 nomena, may be infinite.* 



Nevertheless, I do not agree with M. Comte in condemning those who 

 employ themselves in working out into detail the application of these hy- 

 potheses to the explanation of ascertained facts, provided they bear in 

 mind that the utmost they can prove is, not that the hypothesis zs, but that 

 it may be true. The ether hypothesis has a very strong claim to be so fol- 

 lowed out, a claim greatly strengthened since it has been shown to afford 

 a mechanism which would explain the mode of production, not of light 

 only, but also of heat. Indeed, the speculation has a smaller element of 

 hypothesis in its application to heat, than in the case for which it was 

 originally framed. We have proof by our senses of the existence of molec- 

 ular movement among the particles of all heated bodies ; while we have no 

 similar experience in the case of light. When, therefore, heat is communi- 

 cated from the sun to the earth across apparently empty space, the chain 



* In Dr. Whewell's latest version of his theory (Philosophy of Discovery, p. 331) he makes 

 a concession respecting the medium of the transmission of light, which, taken in conjunction 

 with the rest of his doctrine on the subject, is not, I confess, very intelligible to me, but which 

 goes far toward removing, if it does not actually remove, the whole of the difference between 

 us. He is contending, against Sir William Hamilton, that all matter has weight. Sir Wil- 

 liam, in proof of the contrary, cited the luminiferous ether, and the calorific and electric fluids, 

 "which," he said, "we can neither- denude of their character of substance, nor clothe with 

 the attribute of weight." "To which," continues Dr. Whewell, "my reply is, that precisely 

 because I can not clothe these agents with the attribute of Weight, I do denude them of the 

 character of Substance. They are not substances, but agencies. These Imponderable Agents 

 are not properly called Imponderable Fluids. This I conceive that I have proved." Noth- 

 ing can be more philosophical. But if the luminiferous ether is not matter, and fluid matter, 

 too, what is the meaning of its undulations ? Can an agency undulate ? Can there be al- 

 ternate motion forward and backward of the particles of an agency ? And does not the whole 

 mathematical theory of the undulations imply them to be material ? Is it not a series of de- 

 ductions from the known properties of elastic fluids ? This opinion of Dr. Whewell reduces 

 the undulations to a figure of speech, and the undulatory theory to the proposition which all 

 must admit, that the transmission of light takes place according to laws which present a very 

 striking and remarkable agreement with those of undulations. If Dr. Whewell is prepared 

 to stand by this doctrine, I have no difference with him on the subject. 



