direction of the current is consequently reversed in the circuit,
there is no need to alter the length of the signal currents,
because a momentary current sent in one direction will stand for a
"dot" and in the other direction for a "dash." As a matter of
fact, the code is used in both ways, according to the nature of
the line and receiving instrument. On submarine cables and with
needle and "mirror" instruments, the signals are made by reversing
currents of equal duration, but on land lines worked by "Morse"
instruments and "sounders," they are produced by short and long
currents.

The Morse code is also used in the army for signalling by waving
flags or flashing lights, and may also be serviceable in private
life. Telegraph clerks have been known to "speak" with each other
in company by winking the right and left eye, or tapping with
their teaspoon on a cup and saucer. Any two distinct signs,
however made, can be employed as a telegraph by means of the Morse
code, which runs as shown in figure 46.

The receiving instruments R R' may consist of a magnetic needle
pivotted on its centre and surrounded by a coil of wire, through
which the current passes and deflects the needle to one side or
the other, according to the direction in which it flows. Such was
the pioneer instrument of Cooke and Wheatstone, which is still
employed in England in a simplified form as the "single" and
"double" needle-instrument on some of the local lines and in
railway telegraphs. The signals are made by sending momentary
currents in opposite directions by a "double current" key, which
(unlike the key K in figure 45) reverses the poles