"
"Well?" I queried, endeavouring to follow him.
"The electric arc," he continued, "isn't always just a silent
electric light. You know that. You've heard them make noises.
Under the right conditions such a light can be made to talk--the
'speaking arc,' as Professor Duddell calls it. In other words, an
arc light can be made to act as a telephone receiver."
I could hardly believe the thing possible, but Garrick went on
explaining.
"You might call it the arcophone, I suppose. The scientific fact
of the matter is that the arc is sensitive to very small
variations of the current. These variations may run over a wide
range of frequency. That suggested to Duddell that a direct-
current arc might be used as a telephone receiver. All that you
need is to add a microphone current to the main arc current. The
arc reproduces sounds and speech distinctly, loud enough, even, to
be heard several feet away from the light."
He had cut out the microphone again while he was talking to me.
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