Chapter I. A Man on the Roof

"Tom, I don't believe it can be done!"

"But, Dad, I'm sure it can!"

Tom Swift looked over at his father, who was seated in an easy chair in the library. The elderly gentleman--his hair was quite white now--slowly shook his head, as he murmured again:

"It can't be done, Tom! It can't be done! I admit that you've made a lot of wonderful things--things I never dreamed of--but this is too much. To transmit pictures over a telephone wire, so that persons cannot only see to whom they are talking, as well as hear them--well, to be frank with you, Tom, I should be sorry to see you waste your time trying to invent such a thing."

"I don't agree with you. Not only do I think it can be done, but I'm going to do it. In fact, I've already started on it. As for wasting my time, well, I haven't anything in particular to do, now that my giant cannon has been perfected, so I might as well be working on my new photo telephone instead of sitting around idle."

"Yes, Tom, I agree with you there," said Mr. Swift. "Sitting around idle isn't good for anyone--man or boy, young or old. So don't think I'm finding fault because you're busy."

"It's only that I don't want to see you throw away your efforts, only to be disappointed in the end. It can't be done, Tom, it can't be done," and the aged inventor shook his head in pitying doubt.

Tom only smiled confidently, and went on:

"Well, Dad, all you'll have to do will be to wait and see. It isn't going to be easy--I grant that. In fact, I've run up against more snags, the little way I've gone so far, than I like to admit. But I'm going to stick at it, and before this year is out I'll guarantee, Father, that you can be at one end of the telephone wire, talking to me, at the other, and I'll see you and you'll see me--if not as plainly as we see each other now, at least plainly enough to make sure of each other."

Mr. Swift chuckled silently, gradually breaking into a louder laugh. Instead of being angry, Tom only regarded his father with an indulgent smile, and continued:

"All right, Dad. Go ahead, laugh!"

"Well, Tom, I'm not exactly laughing at you--it's more at the idea than anything else. The idea of talking over a wire and, at the same time, having light waves, as well as electrical waves passing on the same conductor!"

"All right, Dad, go ahead and laugh. I don't mind," said Tom, good-naturedly. "Folks laughed at Bell, when he said he could send a human voice over a copper spring; but Bell went ahead and to-day we can talk over a thousand miles by wire. That was the telephone."

"Folks laughed at Morse when he said he could send a message over the wire. He let 'em laugh, but we have the telegraph. Folks laughed at Edison, when he said he could take the human voice--or any other sound--and fix it on a wax cylinder or a hard-rubber plate--but he did it, and we have the phonograph. And folks laughed at Santos Dumont, at the Wrights, and at all the other fellows, who said they could take a heavier-than-air machine, and skim above the clouds like a bird; but we do it--I've done it-- you've done it."

"Hold on, Tom!" protested Mr. Swift. "I give up! Don't rub it in on your old dad. I admit that folks did laugh at those inventors, with their seemingly impossible schemes, but they made good. And you've made good lots of times where I thought you wouldn't. But just stop to consider for a moment. This thing of sending a picture over a telephone wire is totally out of the question, and entirely opposed to all the principles of science."

"What do I care for principles of science?" cried Tom, and he strode about the room so rapidly that Eradicate, the old colored servant, who came in with the mail, skipped out of the library with the remark:

"Deed, an' Massa 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 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 each other. It would be a dead sure thing then. And Mr. Brown wouldn't have to take Mr. Smith's word that it was he who was talking. He could even get witnesses to look at the wire-image if he wanted to, and so clinch the thing. It will prevent a lot of frauds."

"Well, Tom, maybe you're right. Go ahead. I'll say no more against your plans. I wish you all success, and if I can help you, call on me."

"Thanks, Dad. I knew you'd feel that way when you understood. Now I'm going--"

But what Tom Swift was going to do he did not say just then, for above the heads of father and son sounded a rattling, crashing noise, and the whole house seemed to shake Then the voice of Eradicate was heard yelling:

"Good land! Good land ob massy! Come out yeah, Massa Tom! Come right out yeah! Dere's a man on de roof an' he am all tangled up suthin' scandalous! Come right out yeah befo' he falls and translocates his neck! Come on!"