"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."