Besides, there
may be only one of them."
"Then what is this?" I asked.
"Well," he argued, "they certainly can't work without light of
some kind, can they?"
I acquiesced.
"This is an instrument which literally makes light audible," he
pursued.
"Hear light?" I repeated, in amazement.
"Exactly," he reiterated. "You've said it. It was invented to
assist the blind, but I think I'll be able to show that it can be
used to assist justice--which is blind sometimes, they say. It is
the optophone."
He paused to adjust the thing more accurately and I looked at it
with an added respect.
"It was invented," he resumed, "by Professor Fournier d'Albe, a
lecturer on physics at the University of Birmingham, England, and
has been shown before many learned societies over there."
"You mean it enables the blind to see by hearing?" I asked.
"That's it," he nodded. "It actually enables the blind to locate
many things, purely by the light reflected by them. Its action is
based on the peculiar property of selenium, which, you probably
know, changes its electrical conductivity under the influence of
light.
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