346 



SCIENTIFIC THOUGHT. 



26. 



Molecular 

 action. 



Nevertheless, the fact that gravity, radiation, and 

 electric and magnetic action appear as central emana- 

 tions, decreasing with the square of the distance, two 

 properties which lend themselves to mathematical and 

 geometrical representation, seemed to pave the way for 

 further generalisations. All forces in nature were put 

 down as central forces, either attractive or repulsive, and 

 if not following the Newtonian formula, still dependent on 

 the distance according to some mathematical expression. 

 For nearly a century theoretical physics were occupied in 

 working out the mathematical formulae expressive of these 

 ideas, and Laplace himself promoted these attempts by the 

 weight of his great authority. We do not possess the final 

 views on this point with which the great mathematician 

 intended to complete the last edition of his ' Exposition 

 du Systeme du Monde ' ; but some of the later chapters of 

 this work, treating of gravitation and molecular attraction, 

 show us clearly in which direction he looked for progress 

 in theoretical physics. 1 



no peculiar condition of the inter- 

 vening or diamagnetic matter ; but 

 now that we are able to distinguish 

 such an action ; . . . now that 

 diamaguetics are shown not to be 

 indifferent bodies, I feel still more 

 confidence in ... asking whether 

 it may not be by the action of the 

 contiguous or next succeeding par- 

 ticles that the magnetic force is 

 carried onward," &c. (No. 24.43). 

 Faraday also made repeated experi- 

 ments with the view of determin- 

 ing how the force of gravitation 

 is communicated, believing as little 

 as Newton did in an actio in distans, 

 and he was wont to quote New- 

 ton's words on this matter, refer- 

 ring also to Euler's ether theory 

 (No. 3305). 



1 In the fifth edition of the ' Ex- 

 position du Systeme du Monde' La- 

 place had suppressed these chapters, 

 and had announced his intention 

 "to unite the principal results of 

 the application of analysis to phe- 

 nomena depending on a molecular 

 action differing from universal at- 

 traction" into a special treatise 

 which should form a sequel to the 

 'Exposition,' &c. This project was 

 never carried out (see "avertisse- 

 ment au sixieme edition de ' 1'Ex- 

 position ' "). The success which 

 attended Laplace's attempts to ex- 

 plain double refraction and aber- 

 ration of light (following Newton's 

 suggestions in the ' Principia ' and 

 ' Optics ') as well as capillary pheno- 

 mena (following Haukesbee) left no 



