io6 POPULAR SCIENCE MONTHLY. 



in the plane of the radiator, and secondly, the lines of magnetic flux 

 at right angles to these. At any one point in space these two changes, 

 the strain and the flux, succeed each other periodically, being, however, 

 at right angles in direction. At any one moment these two effects are 

 distributed periodically or cyclically through space, and these changes 

 in time and space constitute an electric wave or electromagnetic wave. 



We may then summarize the above statements by saying that the 

 most recent hypothesis as to the nature of electrical action and of 

 electricity itself is briefly comprised in the following statements: The 

 universally diffused medium called the ether has had created in it 

 certain centers of strain or radiating points from which proceed lines 

 of strain, and these centers of force are called electrons. Electrons 

 must, therefore, be of two kinds, positive and negative, according to 

 the direction of the strain radiating from the center. These electrons 

 in their free condition constitute what we call electricity, and the elec- 

 trons themselves are the atoms of electricity which, in one sense, is, 

 therefore, as much material as that which we call ordinary gross or 

 ponderable matter. 



Collocations of these electrons constitute the atoms of gross mat- 

 ter, and we must consider that the individuality of any atom is not 

 determined merely by the identity of the electrons composing it, but 

 by the permanence of their arrangement or form. In any mass of 

 material substance there is probably a continual exchange of electrons 

 from one atom to another, and hence at any one given moment, whilst 

 a number of the electrons are an association forming material atoms, 

 there will be a further number of isolated but intermingled electrons, 

 which are called the free electrons. In substances which we call good 

 conductors, we must imagine that the free electrons have the power of 

 moving freely through or between the material atoms, and this move- 

 ment of the electrons constitutes a current of electricity; whilst a 

 superfluity of electrons of either type in any one mass of matter con- 

 stitutes what we call a charge of electricity. Hence an electrical oscil- 

 lation, which is merely a very rapid alternating current taking place in 

 a conductor, is on this hypothesis assumed to consist in a rapid move- 

 ment to and fro of the free electrons. We may picture to ourselves, 

 therefore, a rod of metal in which electrical oscillations are taking 

 place, as similar to an organ pipe or siren tube in which movements 

 of the air particles are taking place to and fro, the free electrons cor- 

 responding with the air particles. 



Owing to the nature of the structure of an electron, it follows, 

 however, that every movement of an electron is accompanied by changes 

 in the distribution of the electric strain or ether strain taking place 

 throughout all surrounding space, and, as already explained, certain 

 very rapid movements of the electrons have the effect of detaching 



