370 



SCIENTIFIC THOUGHT. 



point I wish to urge is, how in those clays the Newtonian 

 formula was taken as the great model of a law of nature, 

 and how the researches of Coulomb, Poisson, Ampere, and 

 Weber stand in logical connection with the theory of 

 gravitation. Let us see what Weber himself says on this 

 subject : l " After the general laws of motion had fur- 



chosen. This explains the fact, 

 deplored by Weber's friends and 

 admirers, that his name has dropt 

 out of the list of terms now adopted 

 throughout the civilised world. (See 

 Wiedemann, ' Die Electricitat, ' 

 Braunschweig, 1885, vol. iv. p. 

 906, &c.) Recently Prof. Lodge 

 has suggested the introduction of 

 the names of Weber and Gauss to 

 denote some of the derived units in 

 the electrical measurements. See 

 Brit. Assoc. Report, 1895, p. 197 n. 

 1 Weber's theoretical conception 

 of the nature of electric action at a 

 distance is mixed up with his exact 

 measurements of electrical quanti- 

 ties, though these can be stated 

 without making use of his theoreti- 

 cal conceptions. It is the nature 

 of the absolute system of measure- 

 ment that it establishes numeri- 

 cal relations based upon a small 

 number of original units (space, 

 time, and mass, or space and time 

 alone, see note to p. 323 above) 

 which are universally intelligible. 

 Whatever, therefore, the theoretical 

 views may be which led the investi- 

 gation, in the end these are elim- 

 inated in the system of original 

 (primary) and derived (secondary) 

 units. But Weber's theory com- 

 mands attention for its own sake 

 as the furthest stage to which 

 the gravitational view of phenom- 

 ena, provisionally introduced by 

 Newton, has been pushed. It has 

 been extolled and condemned, ac- 

 cording to the favour with which 

 the purely mathematical treatment 

 of phenomena has been received. 



In the school of Laplace this purely 

 mathematical treatment quite ob- 

 scured all other views which did 

 not minister to it. Thus Laplace 

 remained to the end an adherent of 

 the emission or corpuscular theory 

 of light, and opposed the ideas of 

 Young and Fresnel, who developed 

 the dynamical view. In order to 

 make the cosmical view of nature 

 useful for the explanation of mole- 

 cular phenomena, two distinct and 

 definite conceptions, contained in 

 the gravitation formula, had to be 

 modified and enlarged. The con- 

 ception of matter, which in physical 

 astronomy is limited to gravitational 

 matter, had to be extended so as to 

 bring into calculation what was then 

 called imponderable matter, such as 

 light, heat, and electricity. And 

 the law of gravitation, which defines 

 the purely attractive property of 

 ponderable matter, had to be modi- 

 fied so as to embrace also the repul- 

 sive action observable in a certain 

 class of phenomena. Coulomb had 

 shown that ponderable matter 

 charged with electricity followed 

 the same formula for attraction 

 and repulsion as gravitating bodies 

 did : he simply adopted the two- 

 fluid theory of electric matter. 

 Poisson developed the mathematics 

 of fluids, actuated byrepelling forces 

 depending on the inverse square of 

 the distance. Oersted showed the 

 action of electric currents on mag- 

 nets ; and Ampere showed that 

 magnets can in their action be sup- 

 planted by electric currents. La- 

 place very early satisfied himself that 



