Page:Popular Science Monthly Volume 63.djvu/113

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109
HERTZIAN WAYE WIRELESS TELEGRAPHY.

Fig. 6. (a) Distribution OF Electric Pressure in a Marconi Aerial A, (b) Dis- tribution OF Electric Current in a Marconi Aerial, as shown by the

along the aerial by the ordinates of a dotted line so drawn that its dis- tance from the aerial represents the potential oscillation or current oscillation at that point (see Fig. 6).

This distribution of potential and current along the wire does not necessarily imply that any one electron moves far from its normal posi- tion. The actual movement of any particular air molecule in the case of a sound wave is prob- ably very small, and reckoned in millionths of an inch. So also we must suppose that any one electron may have a small individual amplitude of movement, but the displacement is transferred from one to another. Conduction in a solid may be effected by the movement of free electrons intermingled with the chemical atoms, but any one electron may be continually passing from a condition of freedom to one of combination.

So much for the events inside the wire, but now outside the wire its electric charge is repre- sented by lines of electric strain springing from the aerial to the earth. It must be remem- bered that every line of strain terminates on ordinates of the dotted

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an electron or a co-electron. Hence when the

discharge or spark takes place between the spark balls, the rapid move- ment of the electrons in the wire is accompanied by a redistribution and movement of the lines of strain outside. As the negative charge flows out of the aerial the ends of the strain lines abutting on to it run down the wire and are transferred to the earth, and at the next instant this semi-loop of electric or ether strain, with its ends on the earth, is pushed out sideways from the wire by the growth of a new set of lines of ether strain in an opposite direction. The process is best under- stood by consulting a series of diagTams which represent the distribu- tion and approximate form of a few of the strain lines at successive instants (see Fig. 7). In between the lines of formation of the suc- cessive strain lines between the aerial and the earth, corresponding to the successive alternate electric charges of the aerial with opposite sign, there are a set of concentric rings of magnetic flux formed round it which are alternately in opposite directions, and these expand out, keeping step with the progress of the detached strain loops and having their planes at right angles to the latter. As the semi-loops of electric strain march outwards with their feet on the ground, these strain lines must always be supposed to terminate on electrons, but not continually on the same electrons. Since the earth is a conductor, we must sup- pose that there is a continual migration of the electrons forming the