These two photographs show the most modern form of the instruments
which, as we are told on another page, were invented in England by
Wheatstone and Cooke. In sending a paper tape is punched in what
is called a perforator, which has a keyboard like a typewriter. A
certain combination of holes means a certain letter. This tape is then
automatically fed through the sending instrument, which sends impulses
over the wire. The tape with the holes punched through it can be seen
in the picture.
On the right is the Wheatstone receiving instrument. It prints the
signals received in dots and dashes on a tape, which is translated by
the operator who typewrites the translation on a message blank for
delivery.]
[Illustration: The automatic telegraph typewriter shown here is one of
the wonderful instruments mentioned on one of the preceding pages. The
operator at the other end of the line writes on a typewriter keyboard,
on the sending instrument. The electric impulses are received by the
machine shown above, which automatically typewrites the message on a
blank, ready for delivery.]
On this page we see some of the first telegraph instruments, in
fact, the very instruments which Professor Morse used in the early
demonstrations of his invention. These instruments may be seen in the
Smithsonian Institution at Washington, D. C. The key is known as the
Vail key, because it is supposed to have been constructed by Alfred
Vail, who worked with Morse in his experiments with the telegraph. As
can be seen it is very simple. One wire was connected to the spring
piece and the other to the post beneath it. When the key was pressed
down, the contact was made and an impulse sent over the wire, either a
dot, if the key was pressed down and immediately released, or a dash if
it were held down for just the fraction of a second before releasing.
From the very first it was found that relays were necessary, because
the current after coming a long way over the wire often was not
strong enough to operate the recording instrument. Therefore, this
weak current was made to go though the electro-magnets of the relay,
magnetizing these and pulling to the left the upright arm which can be
seen in the photograph with a little block of iron attached to it. This
arm, when pulled by the magnets, made a contact at the top and allowed
a strong current from a battery to flow through the magnets of the
recording instrument.
The first practical recording telegraph instrument devised by Morse
is shown. It looks like a clumsy affair compared to the instruments
of to-day, but it worked so effectively as to convince people of the
possibilities of the great invention. In the wooden box, attached to
the frame at the right, is clockwork which pulled a paper tape at an
even rate of speed over a pulley just beneath a needle point. This
needle point is attached to a light framework having a piece of iron
fastened in it. Below this iron are the electro-magnets, and when they
received an impulse of current from the battery, through the relay,
they pulled down the frame so that the point made a mark upon the paper
tape which moved under it. Thus in the tape appeared a series of dots
and dashes, which the operator, knowing the Morse Code, could easily
translate into English.
[Illustration: THE FIRST TELEGRAPH INSTRUMENTS