Here, the mouthpiece is just a shell
supporting a thin metal diaphragm to which the mirror on the back
is attached, an apparatus for transforming the air vibrations
produced by the voice into light vibrations of the projected beam,
which is reflected from this light here in the room. The light
reflected is thus thrown into vibrations corresponding to those in
the diaphragm."
"And then?" I asked impatiently.
"That varying beam of light shoots out of this room, and is caught
by the huge reflector which you saw me set up at the foot of that
tall tree which you can just see against the dark sky over there.
That parabolic mirror gathers in the scattered rays, focusses them
on the selenium cell which you saw in the middle of the reflector,
and that causes the cell to vary the amount of electric current
passing through it from a battery of storage cells. It is
connected with a very good telephone receiver. Every change in the
beam of light due to the vibrations of my voice is caught by that
receiving mirror, and the result is that the diaphragm in the
receiver over there which Dillon is holding to his ear responds.
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