Page:Tom Swift and His Photo Telephone.djvu/14

8 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 males 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?"