rtia of this current causes it to overshoot
the mark, and for an instant the charge of the jar is reversed; the
current now flows backward and charges the jar up as at first; back
again flows the current, and so on, charging and reversing the charge
with rapid oscillations until the energy is all dissipated into heat.
The operation is precisely analogous to the release of a strained
spring or to the plucking of a stretched string.

But the discharging body thus thrown into strong electrical vibration
is embedded in the all-pervading ether, and we have just seen that the
ether possesses the two properties requisite for the generation and
transmission of waves--viz., elasticity and inertia or density; hence,
just as a tuning fork vibrating in air excites aerial waves or sound,
so a discharging Leyden jar in ether excites ethereal waves or light.

Ethereal waves can therefore be actually produced by direct electrical
means. I discharge here a jar, and the room is for an instant filled
with light. With light, I say, though you can see nothing. You can see
and hear the spark indeed--but that is a mere secondary disturbance we
can for the present ignore--I do not mean any secondary disturbance. I
mean the true ethereal waves emitted by the electric oscillation going
on in the neighborhood of this recoiling dielectric. You pull aside
the prong of a tuning fork and let it go; vibration follows and sound
is produced. You charge a Leyden jar and let it discharge; vibration
follows and light is excited.

It is light just as good as any other light. It travels at the same
pace, it is reflected and refracted according to the same laws; every
experiment known to optics can be performed with this ethereal
radiation electrically produced, and yet you cannot see it. Why not?
For no fault of the light; the fault (if there be a fault) is in the
eye. The retina is incompetent to respond to these vibrations--they
are too slow. The vibrations set up when this large jar is discharged
are from a hundred thousand to a million per second, but that is too
slow for the retina. It responds only to vibrations between 4,000
billions and 7,000 billions per second. The vibrations are too quick
for the ear, which responds only to vibrations between 40 and 40,000
per second. Between the highest audible and the lowest visible
vibrations there has been hitherto a great gap, which these electric
oscillations go far to fill up. There has been a great gap s