Tom Swift and His Photo Telephone | Page 5

Tom must be pow'fully preragitated dis mawnin'!"
"Some of the scientists said it was totally opposed to all natural laws
when I planned my electric rifle," went on Tom. "But I made it, and it
shot. They said my air glider would never stay up, but she did."
"But, Tom, this is different. You are talking of sending light
waves--one of the most delicate forms of motion in the world--over a
material wire. It can't be done!"
"Look here, Dad!" exclaimed Tom, coming to a halt in front of his
parent. "What is light, anyhow? Merely another form of motion; isn't
it?"
"Well, yes, Tom, I suppose it is."
"Of course it is," said Tom. "With vibrations of a certain length and
rapidity we get sound--the faster the vibration per second the higher the
sound note. Now, then, we have sound waves, or vibrations, traveling
at the rate of a mile in a little less than five seconds; that is, with the air
at a temperature of sixty degrees. With each increase of a degree of
temperature we get an increase of about a foot per second in the
rapidity with which sound travels."
"Now, then, light shoots along at the rate of 186,000,000 miles a
second. That is more than many times around the earth in a second of
time. So we have sound, one kind of wave motion, or energy; we have
light, a higher degree of vibration or wave motion, and then we come to
electricity--and nobody has ever yet exactly measured the intensity or
speed of the electric vibrations."
"But what I'm getting at is this--that electricity must travel pretty nearly
as fast as light--if not faster. So I believe that electricity and light have
about the same kind of vibrations, or wave motion."
"Now, then, if they do have--and I admit it's up to me to prove it," went

on Tom, earnestly--"why can't I send light-waves over a wire, as well
as electrical waves?"
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 sensitive 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