Tom Swift and His Photo Telephone | Page 5

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 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