Mr. Swift was silent for a moment. Then he said, slowly:

"Well, Tom, I never heard it argued just that way before. Maybe
there's something in your photo telephone after all. But it never
has been done. You can't deny that!"

He looked at his son triumphantly. It was not because he wanted to
get the better of him in argument, that Mr. Swift held to his own
views; but he wanted to bring out the best that was in his
offspring. Tom accepted the challenge instantly.

"Yes, Dad, it has been done, in a way!" he said, earnestly. "No
one has sent a picture over a telephone wire, as far as I know,
but during the recent hydroplane tests at Monte Carlo, photographs
taken of some of the events in the morning, and afternoon, were
developed in the evening, and transmitted over five hundred miles
of wire to Paris, and those same photographs were published in the
Paris newspapers the next morning."

"Is that right, Tom?"

"It certainly is. The photographs weren't so very clear, but you
could make out what they were. Of course that is a different
system than the one I'm thinking of. In that case they took a
photograph, and made a copper plate of it, as they would for a
half-tone illustration. This gave them a picture with ridges and
depressions in copper, little hills and valleys, so to speak,
according to whether there were light or dark tints in the
picture. The dark places meant that the copper lines stood up
higher there than where there were light colors."

"Now, by putting this copper plate on a wooden drum, and revolving
this drum, with an electrical needle pressing lightly on the
ridges of copper, they got a varying degree of electrical current.
Where the needle touched a high place in the copper plate the
contact was good, and there was a strong current. When the needle
got to a light place in the copper--a depression, so to speak--the
contact was not so good, and there was only a weak current."

"At the receiving end of the apparatus there was a sensitized film
placed on a similar wooden drum. This was to receive the image
that came over the five hundred miles of wire. Now then, as the
electrical needle, moving across the copper plate, made electrical
contacts of different degrees of strength, it worked a delicate
galvanometer on the receiving end. The galvanometer caused a beam
of light to vary--to grow brighter or dimmer, according as the
electrical current was stronger or weaker. And this light, falling
on the se