in Causal Research. 357 



the value of mathematics in physical inquiries. Its achieve- 

 ments, when resting on definite physical conceptions, may be 

 illustrated by the splendid results of the kinetic theory of 

 gases ; its complete powerlessness, in the absence of such con- 

 ceptions, may be equally well exemplified by the inquiry as 

 to the constitution of the aether. Nowhere, perhaps, have the 

 spiritualistic assumptions about "force"* been so indiscrimi- 

 nately applied as here, to the complete exclusion of all that 

 can be called clear physical conceptions. This has naturally 

 resulted from the fatal step taken at the time of Newton, of 

 putting forward that notion of " action at a distance," which 

 he characterized as a " great absurdity," and out of which 

 inevitably sprang the endless train of "forces ;" of which it 

 is aptly remarked by the writer of the article on " the Atomic 

 Theory of Lucretius " (North British Review, March 1868, 

 page 239): — "This idea of the constitution of matter was 

 perhaps the worst of all No attempt was made to show- 

 how or why the forces acted ; but gravitation being taken as 

 due to a mere ' force,' speculators thought themselves at 

 liberty to imagine any number of forces, attractive or repul- 

 sive, or alternating, varying as the distance, or the square, 

 cube, fifth power of the distance, &c." 



Sir W. Thomson observes on the waste of mathematical 

 skill due to the speculations about "force," much in the fol- 

 lowing terms f : — " The eighteenth century forms a scientific 

 school of its own, where in place of the not unnatural asser- 

 tion of the ancient schoolmen — ' a body cannot act where it 

 is not,'' the most extraordinary of all paradoxes was set up — 

 ' contact does not exist/ This strange notion took deep root ; 

 and out of it sprang a barren tree, which exhausted the 

 ground and overshadowed the whole field of molecular phy- 

 sics, and upon which so much useless work of the great mathe- 



* It will perhaps be said that the notion of " force " (in the sense of an 

 action across space without the intervention of matter) (s now almost 

 abandoned, at least in this country. But then there is a great difference 

 between the mere tacit relinquishment of an assumption or theory and 

 that practical indication of its complete rejection which is afforded by the 

 stirring-up of the mind to active inquiry and realization of the physical 

 conditions that can alone replace the assumption. That this result is far 

 from being generally attained yet, more especially in regard to that which 

 must be expected as to the functions of the aether, where the physical 

 deductions inevitably following on the rejection of " force" would be of 

 immense practical interest, I think I shall sufficiently prove in the sequel. 

 Indeed it will become apparent that the former vast influence of the notion 

 of " force " still remains almost undiminished in relation to the aether. 



t I translate conveniently from a German quotation (that I happen to 

 have by me) from the work ' Reprint of Papers on Electrostatics and 

 Magnetism,' 1872. 



