CHAPTER X. 



THE ELECTRON THEORY. 



136. The mechanical theory of electricity and the atomic 

 theory of electricity. The study of electricity and magnetism as 

 represented in the foregoing chapters is independent of any con- 

 sideration of the nature of the physical action which leads to the 

 production of electromotive force in a voltaic cell or dynamo; it 

 is independent of any consideration of the nature of the physical 

 action which constitutes an electric current in a wire; it is inde- 

 pendent of any consideration of the nature of the disturbance 

 which constitutes a magnetic field; and it is independent of any 

 consideration of the nature of the disturbance or stress which 

 constitutes an electric field. This kind of study of electricity 

 and magnetism may very properly be called electro-mechanics. 



Simple mechanics is the study of ordinary bodies at rest or in 

 visible motion, and one of the most important ideas in mechanics 

 is the idea of force ; but the science of mechanics is not concerned 

 with, and indeed it sheds no light upon the question as to the 

 physical nature of force. Thus, the science of mechanics is not 

 concerned with the question as to the nature of the action which 

 takes place in a gas and causes the gas to exert a force on a piston ; 

 the science of mechanics is not concerned with the question as to 

 the nature of the action which takes place in the material of a 

 stretched wire causing the wire to exert a pull upon each of the 

 two supports at its ends; the science of mechanics is not con- 

 cerned with the nature of the action between the earth and a 

 heavy weight which causes the earth to exert a force on the 

 weight; the science of mechanics is not concerned with the 

 nature of the action which takes place between two bodies 

 which slide over each other and which leads to the production of 

 the force of friction. It is sufficient for the science of mechanics 



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