THE ELECTRON THEORY. 275 



that these actions are what may be called states of permanency 

 of the respective systems. To speak of these actions as states 

 of permanency is to call to mind the fact that they remain un- 

 changed under given conditions. To say that a gas in a cylinder 

 pushes with a force of 100 pounds on the piston thus compressing 

 a spring is to refer to a state of affairs in which there is a clearly 

 defined and maintained relationship between the condition of the 

 spring and the condition of the gas. The science of mechanics 

 owes its existence to the legitimacy and usefulness of the idea of 

 force irrespective of the nature of the physical process upon 

 which force action depends. 



Similarly it is sufficient for the science of electro-mechanics 

 that the physical actions that underlie electromotive force, 

 electric current, magnetic field and electric field are what may 

 be called states of permanency. Thus to say that a dynamo 

 produces a current of 100 amperes through a circuit is to refer 

 to a state of affairs in which there is a definite and main- 

 tained relationship between the dynamo and the circuit, the 

 dynamo delivers energy at a certain rate and the circuit receives 

 energy at a certain rate, and the circuit exhibits to a definite 

 degree the various effects which are associated with what we call 

 an electric current. The science of electro-mechanics owes its 

 existence to the legitimacy and usefulness of the ideas of electro- 

 motive force, electric current, magnetic field and electric field 

 irrespective of the nature of the physical actions upon which 

 these various things depend. 



The superficial character of the science of simple mechanics 

 and of the science of electromechanics may be further exemplified 

 as follows: A sample of steel is broken by a tension of 120,000 

 pounds, but the exact character of the action which takes place 

 in the steel when it is placed under tension is not a matter for 

 consideration. Neither does one need to consider the action 

 which takes place in the furnace of the boiler which supplies 

 steam to the engine which drives the dynamo which supplies 

 current to the motor which drives the testing machine ! A plate 



