[Illustration: A LATER AND IMPROVED RECORDING INSTRUMENT.
Here we see some early telegraph instruments which have been improved
somewhat from the crude devices illustrated on the preceding page.
The key answers the same purpose as before, but has been improved by
pivoting the lever arm, and having a coil spring, adjustable by means
of a screw, so that the weight necessary to press it down can be varied
to suit the likings of the operator who uses it. The play of the key
or the distance it must be pressed down before it makes an electric
contact, can be adjusted by another screw.
The recording instrument here shown is a much neater affair than the
cumbersome device which Professor Morse first built. The cumbersome
wooden box has been replaced with a neat brass frame containing the
clockwork for drawing the paper tape beneath the marking point, which
is attached to a piece of iron, or armature, placed just above the
magnet.
Below we see the most modern types of Morse instruments. In the center
is the key, which is not much changed except that it is built to be
low down to a table, so that the operator may rest his forearm on the
table top in front of it, and operate the key with his wrist, with less
fatigue. The relay at the left is interesting. It shows how little this
instrument has changed, except for refinement in its appearance, from
the first relay built by Professor Morse. At the right is the Morse
sounder, which has replaced the old Morse tape recording instrument.
When current goes through the magnets they attract a piece of iron
attached to the metal arm and pull it down to strike the brass frame.
This makes a click, and when the current is intercepted, the magnets
release the arm and a spring pulls it back, making another click. The
operator reads the message by listening to the clicks. If the up click
comes right after the down click it represents a dot. If there is a
pause between them, a dash is represented.]
[Illustration: