It can be read as long as steel
will last. It is as effective for long distances as for short, and
there is wire enough on one of these spools for thirty minutes of
uninterrupted record."
Craig continued to tinker tantalisingly with the machine.
"The principle on which it is based," he added, "is that a mass of
tempered steel may be impressed with and will retain magnetic
fluxes varying in density and in sign in adjacent portions of its
mass. There are no indentations on the wire or the steel disk.
Instead there is a deposit of magnetic impulse on the wire, which
is made by connecting up an ordinary telephone transmitter with
the electromagnets and talking through the coil. The disturbance
set up in the coils by the vibration of the diaphragm of the
transmitter causes a deposit of magnetic impulse on the wire, the
coils being connected with dry batteries. When the wire is again
run past these coils, with a receiver such as I have here in
circuit with the coils, a light vibration is set up in the
receiver diaphragm which reproduces the sound of speech.
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