AND MODERN PHYSICS. 155 



and the 'value and importance of his work was not 

 recognised until tho appearance in 1879 of the 

 * Electrical Researches of Henry Cavendish, 9 ' edited 

 by Clerk Maxwell 



Early in the present century the application of 

 mathematical analysis to electrical problems was 

 begun by Laplace, who investigated the distribution 

 of electricity on spheroids, and about 181 1 Poisson's 

 great work on tho distribution of electricity on two 

 spheres placed at any given distance apart was pub- 

 lished. Meanwhile tho properties of tho electric 

 current were being investigated. Galvani's discovery 

 of the muscular contraction in a frog's leg, caused by 

 tho contact of dissimilar metals, wits made in 1700. 

 Volta invented the voltaic pile in 1800, and Oersted in 

 1820 discovered that an electric current produced 

 magnetic force in its neighbourhood. On this Ampere 

 laid tho foundation of his theory of electro-dynamics, 

 in which he showed how to calculate the forces be- 

 tween circuits carrying currents from an assumed law 

 of force between each jKiir of elements of the circuits. 

 His e.\|>erinients proved that the consequences which 

 follow from this law arc consistent with all the 

 observed facts. They do not prove that Ampere's law 

 alone can explain the facts. 



. Maxwell, writing on this subject in the ' Electricity 

 an I Magnetism," vol. ii., p. 162, says 



44 The c\icriiucntal investigation by which Ampere estab- 

 lished the laws of the mechanical action between electric 

 cun cuts is one of the most brilliant achievements in science. 



44 The whole, theory anil experiment, seems its if it had 

 full grown and full armed from the brain of the 



