106 CONDUCTION AND RADIATION [CH. x. 



great part of Physics to its simplest terms. This 

 fine attempt, made in 1894, involved definite illus- 

 trative conceptions of the structure of an electron, 

 of its size on the theory that inertia is entirely 

 electric, of the velocities with which electrons revolve 

 in the molecule, and generally of an electronic 

 theory of matter : but in absence of knowledge the 

 mass of an electron was then naturally assumed 

 comparable with that of a hydrogen atom. A great 

 amount of suggestive material is to be found in 

 Dr. Larmor's contributions to the Transactions of the 

 Koyal Society for 1894, 5, 7 ; some of them were 

 summarised in the book called Ether and Matter 

 published by the Cambridge University Press in 

 1900. 



Suffice it here to say that the electron constitutes 

 the basis of the whole treatment, and that there is 

 supposed to be no true electric current except electrons 

 in motion. They may move with the atoms, as in 

 the electrolysis of liquids ; they may fly alone, as in 

 rarefied gases ; or they may be handed on from one 

 fixed atom to the next, as in the process of conduction 

 in solids. 



Conduction. 



The possible modes of conduction or transmission 

 of electricity are in fact three, which I may call 

 respectively the bird-seed method, the bullet method, 

 and the fire-bucket method. 



The bird-seed method is adopted in liquids and 

 usually in gases of ordinary density ; it is exempli- 

 fied in electrolysis ; the bird carries the seed with 

 it, and only drops it when it reaches an electrode. 



The bullet method is the method in rarefied gases, 

 as has been clearly realised by aid of the cathode 



