THE ELECTRICAL NATURE OF MATTER. 181 



ency to persist is interesting. This sudden breaking of a cur- 

 rent gives rise to an electrical push, or electro-motive force, 

 far greater than that which maintained the current. The 

 instant the circuit is broken there is a sudden lurch forward 

 of the current which enables it to spring across the break 

 and which gives rise to the spark seen at that point. The 

 more sudden the break the more violent is the spark. This 

 is very like the blow which a high-pressure service water- 

 tap experiences when the flow of water is suddenly arrested 

 by turning the tap. The jar of the water momentum will 

 sometimes burst the pipe. The delay of the current on 

 making the circuit, and its tendency to persist after break- 

 ing it, prevents any very sudden change in the strength of a 

 current. It is this that hinders telephonic communication 

 through very long wires and renders ocean cable telegraphy 

 a comparatively slow operation. In the past, this refusal cf 

 an electric current to undergo any very sudden change has 

 been called the phenomenon of self-induction or, sometimes, 

 quasi-electrical-inertia. We propose, now, to eliminate both 

 the quasi and electrical and to develop the idea that this un- 

 willingness of an electrical current to start or stop is the 

 unwillingness of matter to start or'stop. That, in each case, 

 the phenomenon is due to simple inertia, and that that in- 

 ertia is purely electrical in its nature. 



The idea that inertia is electrical in its origin first took 

 form in a paper by J. J. Thomson, which appeared in the 

 Philosophical Magazine for 1881, and which has since be- 

 come classical. This paper dealt with the properties of a 

 moving charged sphere, and in it Professor Thomson showed 

 that an electrical charge, concentrated on such a moving 

 sphere, must possess inertia due to the electro-magnetic 

 field of force which it creates by its motion in the surround- 

 ing ether. In other words, it will tend to resist change of 



