Page:Popular Science Monthly Volume 63.djvu/107

103
HERTZIAN WAVE WIRELESS TELEGRAPHY.

reader must be referred for the complete demonstration to the writings of Professor J. J, Thomson[1] and Mr. Oliver Heaviside.[2]

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.'[3] As this phenomenon lies at the very root of Hertzian wave wireless telegraphy, we must spend a moment or two in its careful examination.

Let us imagine two metal rods placed in line and constituting what is called a linear oscillator. Let these rods have adjacent ends separated by a very small air space, and let one rod be charged with positive 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 distribution 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.

Fig. 1. Lines of Electric Strain between a Positive and Negative Electron at Rest.

Suppose then that the air gap is destroyed, 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 circular lines of magnetic flux embracing the rods. This external distribution of magnetism constitutes an electric current in the rods produced by the movement of the two opposite electric charges. At this stage it may be explained 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 material 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 magnetic flux, the direction of these lines being reversed each half cycle.

1. See J. J. Thomson, 'Recent Researches in Electricity and Magnetism,' Chapter I., 16.
2. See O. Heaviside, 'Electromagnetic Theory,' Vol. I., p. 54.
3. Wiedemann's Annalen, 36, p. 1, 1889. Or in his republished papers, 'Electric Waves,' p. 137. English translation by D. E. Jones.