nsitive plate, made a picture, just like the one on the
copper plate in Monte Carlo."

"In other words, where the copper plate was black, showing that
considerable printing ink was needed, the negative on the other
end was made light. Then when that negative was printed it would
come out black, because more light comes through the light places
on a photograph negative than through the dark places. And so,
with the galvanometer making light flashes on the sensitive plate,
the galvanometer being governed by the electrical contacts five
hundred miles away, they transmitted a photograph by wire."

"But not a telephone wire, Tom."

"That doesn't make any difference, Dad. It was a wire just the
same. But I'm not going into that just now, though later I may
want to send photographs by wire. What I'm aiming at is to make an
apparatus so that when you go into a telephone booth to talk to a
friend, you can see him and he can see you, on a specially
prepared plate that will be attached to the telephone."

"You mean see him as in a looking-glass, Tom?"

"Somewhat, yes. Though I shall probably use a metal plate instead
of glass. It will be just as if you were talking over a telephone
in an open field, where you could see the other party and he could
see you."

"But how are you going to do it, Tom?"

"Well, I haven't quite decided. I shall probably have to use the
metal called selenium, which is very sensitive to light, and which
makes a good or a poor electrical conductor according as more or
less light falls on it. After all, a photograph is only lights and
shadows, fixed on sensitive paper or films."

"Well, Tom, maybe you can do it, and maybe you can't. I admit
you've used some good arguments," said Mr. Swift. "But then, it
all comes down to this: What good will it be if you can succeed in
sending a picture over a telephone wire?"

"What good, Dad? Why, lots of good. Just think how important it
will be in business, if you can make sure that you are talking to
the party you think you are. As it is now, unless you know the
person's voice, you can't tell that the man on the other end of
the wire is the person he says he is. And even a voice can be
imitated."

"But if you know the person yourself, he can't be imitated. If you
see him, as well as hear his voice, you are sure of what you are
doing. Why, think of the big business deals that could be made
over the telephone if the two parties could not only hear but see
ea