HYPOTHESES. 



33' 



all equally colisisteht with the phe- 

 nomena, may be infinite.* 



Nevertheless, I do not agree with M. 

 Comte in condemning those who em- 

 ploy themselves in working out into 

 detail the application of these hypo- 

 theses to the explanation of ascer- 

 tained facts, provided they bear in 

 mind that the utmost they can prove 

 is, not that the hypothesis is, but that 

 it may be true. The ether hypothesis 

 has a very strong claim to be so fol- 

 lowed out, a claim greatly strength- 

 ened 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 ori- 

 ginally framed. We have proof by 

 our senses of the existence of mole- 

 cular movement among the particles 

 of all heated bodies, while we have 

 no similar experience in the case of 

 light. When, therefore, heat is com- 

 municated from the sun to the earth, 

 across apparently empty space, the 

 chain of causation has molecular mo- 

 tion both at the beginning and end. 

 The hypothesis only makes the mo- 

 tion continuous by extending it to 

 the middle. Now motion in a body 

 is known to be capable of being im- 

 parted to another body contiguous to 

 it ; and the intervention of a hypo- 



* In Dr. Whewell's latest version of this 

 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 intel- 

 ligible to me, but which goes far towards 

 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 

 William, 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 sub- 

 stance nor clothe with the attribute of 

 weight." " To wliich," continues Dr. Whe- 

 well, " my reply is, that precisely because 

 I cannot clothe these agents with the attri- 

 bute of Weight, I do denude them of the 

 character of Substance. They are not 

 substances, but agencies. These Impon- 



thetical elastic fluid occupying the 

 space between the sun and the earth 

 supplies the contiguity which is the 

 only condition wanting, and which 

 can be supplied by no supposition but 

 that of an intervening medium. The 

 .supposition, notwithstanding, is at 

 best a probable conjecture, not a 

 proved truth ; for there is no proof 

 that contiguity is absolutely required 

 for the communication of motion from 

 one body to another. Contiguity does 

 not always exist, to our senses at 

 least, in the cases in which motion 

 produces motion. The forces which 

 go under the name of attraction, 

 especially the greatest of all, gravita- 

 tion, are examples of motion producing 

 motion without apparent contiguity. 

 When a planet moves, its distant 

 satellites accompany its motion. The 

 sun carries the whole solar system 

 along with it in the progress which it 

 is ascertained to be executing through 

 space. And even if we were to ac- 

 cept as conclusive the geometrical 

 reasonings (strikingly similar to those 

 by which the Cartesians defended 

 their vortices) by which it has been 

 attempted to show that the motions 

 of the ether may account for gravita- 

 tion itself, even then it would only 

 have been proved that the supposed 

 mode of production may be, but not 

 that* no other mode can be, the true 



derable Agents are not properly called Im- 

 ponderable Fluids. This I conceive that I 

 have«proved." Nothing can be more philo- 

 sophical. But if the luminiferous ether is 

 not matter, and fluid matter too, what is 

 the meaning of its undulations? Can an 

 agency undulare? Can there be alternate 

 motion forward and backward of the par- 

 ticles of an agency? And does not the 

 whole mathematical theory of the undula- 

 tions imply them to be material ? Is it not 

 a series of deductions from the known pro- 

 perties 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 transmis-sion of light takes place 

 according to laws which present a very 

 striking and remarkable agreement with 

 those of undulations. If Dr. Whewell if 

 prepared to stand by this doctrine, I hava 

 no difference with him on the subject. 



