HERTZIAN WAVE WIRELESS TELEGRAPHY. 103 



reader must be referred for the complete demonstration to the writings 

 of Professor J. J, Thomson* and Mr. Oliver Heaviside.f 



In the third case, when the electron vibrates, we have a state in 

 which self-closed lines of electric strain and magnetic flux are thrown 

 off and move away through the ether, constituting electric radiation. 

 The manner in which this happens was first described by Hertz in a 

 paper on 'Electric Oscillations treated according to the Method of 

 Maxwell. 'I As this phenomenon lies at the very root of Hertzian 

 wave wireless telegraphy, we must spend a moment or two in its care- 

 ful examination. 



Let us imagine two metal rods placed in line and constituting what 

 is called a linear oscillator. Let these rods have adjacent ends sepa- 

 rated by a very small air space, and let one rod be charged with posi- 

 tive and the other with negative electricity. On the electronic theory 

 this is explained by stating that there is an accumulation of electrons 

 in one and of co-electrons in the other. These charges create a distri- 

 bution of electric strain throughout their neighborhood, which follows 

 approximately the same law of distribution as the lines of magnetic 

 force of a bar magnet, and may be roughly represented as in Fig. 1. 

 Suppose then that the air gap is de- 

 stroyed, these charges move towards 

 each other and disappear by uniting, 

 the lines of electric strain then collapse, 

 and as they shrink in give rise to cir- 

 cular lines of magnetic flux embracing 

 the rods. This external distribution 

 of magnetism constitutes an electric 

 current in the rods produced by the fig.i. lines ^Telectric strain 

 movement of the two opposite electric between a positive and negative 



1 * J , 1 . , . , , Electron at Best. 



Charges. At this stage it may be ex- 

 plained that the electrons or atoms of electricity can in some cases 

 make their way freely between the atoms of ponderable matter. The 

 former are incomparably smaller than the latter, and in those cases in 

 which this electronic movement can take place easily, we call the mate- 

 rial a good conductor. 



Suppose then the electric charges reappear in reversed positions 

 and go through an oscillatory motion. The result in the external space 

 would be the alternate production of lines of electric strain and mag- 

 netic flux, the direction of these lines being reversed each half cycle. 



* See J. J. Thomson, ' Recent Researches in Electricity and Magnetism,' 

 Chapter I., 16. 



t See O. Heaviside, ' Electromagnetic Theory,' Vol. I., p. 54. 



X Wiedemann's Annalen, 36, p. 1, 1889. Or in his republished papers, 

 * Electric Waves,' p. 137. English translation by D. E. Jones. 



