212 hertz's experiments. 



served it would be quite natural tluit they should be described as 

 waves of "volume force," especially if the ouly way in which we could 

 detect the presence of these waves was by observing the force exerted 

 on bodies immersed in it, which was proportional to their volumes, and 

 which we happeii to know is really due to differences of pressure at 

 neighboring' points in the air. We do not know what is the structure 

 of the aether that causes it to exert force on electrified bodies, but we 

 know of the existence of this property, and when it is in this state we 

 say that "electric force" exists in it, and we have certain ways by 

 which we can detect the existence of " electric force," one of which is 

 the production of an electric current in a conductor, and the consequent 

 electrification of the conductor, and if this is strong enough we can 

 produce an electric spark bet^veen it and a neighboring conductor. 

 When a conductor is suddenly electrified, the structure of the aether 

 which is described as electric force existing in it travels from its neigh- 

 borhood through the surrounding icther, and this is described as a 

 wave of electric force travelling through the surrounding aether. It is 

 desirable to be quite clear as to what is meant by the term a wave of 

 electric force and what we know about it. We know that it is a region 

 of wther where its structure is the same as in the neighborhood of elec 

 trifled and some other bodies, and owing to which force is exerted on 

 electrified bodies, and electric currents are pi-oduccd in conductors. 



We may then I'easonably expect that, if it is possible to electrify a 

 body alternately positively and negatively in rapid succession, there 

 will be produced all round it waves of electric force — that is, if the 

 electric force is i)ropagiited by, and is due to, a medium surrounding 

 the electrified body, if electrification is a special state of the medium 

 that fills the space between bodies. 



(2) The next question is: How can we reflect these waves? In order 

 to reflect a wave, we must int<'rpose in its way some body that stops it. 

 What sort of bodies stop electric force? Comluctors are known to act 

 as complete screens of electric force, so that a large conducting sheet 

 would naturally be suggested as the best way to reflect waves of elec- 

 tric force, lieflection always occurs when there is a change in the 

 nature of the medium, even though the change is not so great as to 

 stop the wave, and it has long been known that, besides the action of 

 conductors as scieeus of electric force, different non-conductors act 

 differently in reference to electric force by differing in si)ecific inductive 

 capacity. Hence we might expect non-conductors to reflect these 

 waves, although the reflection would probably not be so intense from 

 them as from conductors. Hence this question of how to reflect the 

 waves is pretty easily solved. All this is on the supposition that there 

 really are waves. If electric force exist everywhere simultaneously, 

 of course there will be no waves to reflect, and consequently no loops 

 and nodes produced by the interference of the incident and reflected 

 waves. 



