"
"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.
Pages:
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28