ELECTRIC WAVE TELEGRAPH Y—FLEMING. 165 
electrons.¢. They have a strong resemblance in many ways to the 
vortices or vortex lines, which can be created in a fluid. Moreover, 
just as vortex lines in a fluid can be self-closed or endless, or else 
terminate in little whirlpools on the free surface of the liquid, so lines 
of electric force can form either closed loops, or else have their ends 
terminating, on opposite charges of electricity, that is, on an electron 
at one end and the positive charge of an atom, whatever that may be, 
at the other end. Suppose, then, that the rod is suddenly connected 
to the earth at the bottom end by allowing it to spark to the earth. 
Its electric charge rushes out, that is, the excess or deficit of electrons 
on its surface disappears, and this movement of electricity constitutes 
an electric current flowing into or out of the rod from the earth. The 
electrons, however, possess inertia or mass, hence when they rush out 
of the rod into the earth they not only discharge it, but overdo it, and 
leave the rod with a positive charge. They then rush back again, and 
the process repeats itself, and we thus obtain a rapid ebb and flow of 
electricity into and out of the wire, called a series of electric oscilla- 
tions. Each rush, however, is 
feebler than the last, and there- 
fore the oscillations decay 
away or, as it is termed, are 
damped. The energy repre- 
sented by the initial charge is 
frittered away, partly owing to 
collisions of the electrons and Fic. 2.—Diagrammatic representation of the 
atoms in the rod and spark dur- detachment of semiloops of electric strain 
: : from a simple Marconi antenna. 
ing the movement, and partly 
because the electron radiates or communicates its kinetic energy to 
the medium when it is accelerated or retarded. 
We have next to attend to the effects taking place outside the rod 
or antenna. As the negative charge disappears from the rod owing 
to the removal of the excess of free electrons from its surface the ends 
of the lines of electric force which abut on it and stretch between it 
and the earth glide downwards along the rod and end by forming a 
semiloop of electric force or strain with its ends or feet resting on 
the earth. (See fig. 2.) This arises from the facts that the lines of 
“Cf. Faraday. ‘‘ Experimental Researches in Electricity,’ Vol. III, series 
XXIX, 5273, 3297, and 3299. ‘On Physical Lines of Magnetic Force.” Faraday 
used the expression physical line of force to denote their concrete reality as 
distinguished from a mere geometrical conception. Also in his paper, ‘‘ Thoughts 
on Ray Vibrations,” Phil. Mag., ser. 3, Vol. XXVIII, 1846, he considers that light 
may be a vibration propagated along lines of force. See also J. J. Thomson, 
“Electricity and Matter,” p. 63, for an argument for the physical reality of lines 
of electric force drawn from the ionization of gases by Réntgen rays. 
