On the afternoon of June 2, 1875, we were hard at work on the same old
job, testing some modification of the instruments. Things were badly out
of tune that afternoon in that hot garret, not only the instruments,
but, I fancy, my enthusiasm and my temper, though Bell was as energetic
as ever. I had charge of the transmitters as usual, setting them
squealing one after the other, while Bell was retuning the receiver
springs one by one, pressing them against his ear as I have described.
One of the transmitter springs I was attending to stopped vibrating and
I plucked it to start it again. It didn’t start and I kept on plucking
it, when suddenly I heard a shout from Bell in the next room, and then
out he came with a rush, demanding, “What did you do then? Don’t change
anything. Let me see!” I showed him. It was very simple. The contact
screw was screwed down so far that it made permanent contact with the
spring, so that when I snapped the spring the circuit had remained
unbroken while that strip of magnetized steel by its vibration over the
pole of its magnet was generating that marvelous conception of Bell’s—a
current of electricity that varied in intensity precisely as the air was
varying in density within hearing distance of that spring. That
undulatory current had passed through the connecting wire to the distant
receiver which, fortunately, was a mechanism that could transform that
current back into an extremely faint echo of the sound of the vibrating
spring that had generated it, but what was still more fortunate, the
right man had that mechanism at his ear during that fleeting moment, and
instantly recognized the transcendent importance of that faint sound
thus electrically transmitted. The shout I heard and his excited rush
into my room were the result of that recognition. The speaking telephone
was born at that moment. Bell knew perfectly well that the mechanism
that could transmit all the complex vibrations of one sound could do the
same for any sound, even that of speech. That experiment showed him that
the complex apparatus he had thought would be needed to accomplish that
long dreamed result was not at all necessary, for here was an extremely
simple mechanism operating in a perfectly obvious way, that could do it
perfectly. All the experimenting that followed that discovery, up to the
time the telephone was put into practical use, was largely a matter of
working out the details. We spent a few hours verifying the discovery,
repeating it with all the differently tuned springs we had, and before
we parted that night Bell gave me directions for making the first
electric speaking telephone. I was to mount a small drumhead of
gold-beater’s skin over one of the receivers, join the center of the
drumhead to the free end of the receiver spring and arrange a mouthpiece
over the drumhead to talk into. His idea was to force the steel spring
to follow the vocal vibrations and generate a current of electricity
that would vary in intensity as the air varies in density during the
utterance of speech sounds. I followed these directions and had the
instrument ready for its trial the very next day. I rushed it, for
Bell’s excitement and enthusiasm over the discovery had aroused mine
again, which had been sadly dampened during those last few weeks by the
meagre results of the harmonic experiments. I made every part of that
first telephone myself, but I didn’t realize while I was working on it
what a tremendously important piece of work I was doing.