They said they were going in the
direction opposite from you."
"Well?" I asked, mystified. "What of it? I know all that,
already."
"But Dillon doesn't," replied Garrick, in great excitement now. "I
knew that we should have to have some way of communicating with
him instantly if this fellow proved to be as resourceful as I
believed him to be. So I thought of the radiophone or photophone
of Dr. Alexander Graham Bell. I have really been telephoning on a
beam of light."
"Telephoning on a beam of light?" I repeated incredulously.
"Yes," he explained, feeling now at liberty to talk since he had
delivered his call for help. "You see, I talk into this
transmitter. The simplest transmitter for this purpose is a plane
mirror of flexible material, silvered mica or microscope glass.
Against the back of this mirror my voice is directed. In the
carbon transmitter of the telephone a variable electrical
resistance is produced by the pressure on the diaphragm, based on
the fact that carbon is not as good a conductor of electricity
under pressure as when not.
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