the speed of the driving motor until the
needle K travels in unison with the disc J, making permanent contact with P
on the contact {95} block Q, which is evidenced by the lamp L remaining
alight. If, however, the needle travels faster than the disc J, contact
with P is broken and fresh contact is made with P^2, the lamp L is
extinguished and the red lamp L^2 lights up, and remains alight until the
operator reduces the speed. Similarly, too, if the needle travels slower
than J, contact is made with P^1, and the circuit of the blue lamp L^1 is
completed. When the speed is either above or below the normal, the needle K
engages with one or the other of the pins D, and as the tension of the
driving belt is only such as is required to drive the needle, the belt
slips on the pulleys until the normal speed is regained.

METHOD OF WORKING

The clockwork motor M, Fig. 51, should be capable of running for several
hours with one winding, and powerful enough to take up the work of driving
the machine without any appreciable effort. The main spindle of the motor
is so arranged that it makes one revolution in two minutes, and the
reduction in speed between the motor shaft and the shaft to which the
coupling A is attached is 30:1. The metal line print having been wrapped
round the drum of the machine, the stylus is put into position, at the edge
of the lap, and with the needle resting about half-way on {96} the margin
of the bare foil left at the commencing edge of the print. Now, when the
two stations are in perfect readiness for work, the motors are started and
the speed adjusted; the speed of the machine being just under one
revolution in four seconds.

[Illustration: FIG. 51.

M, clockwork motor; S, isochroniser; E, friction break; T, brushes; F,
electric clutch; X, gearing; D, D^1, switches; A, flexible coupling; K,
polarised relay; L, circuit breaker; B_1, B_2, B_3, batteries; P, electric
clock; W, terminals for connection to telephone relay; H, terminals for
connection to terminals J, on transmitting machine.]

The switch D is then closed, and the arm of the switch D^1 placed on the
contact stud (1), at the transmitting station only. As soon as the switches
are closed the clutch F comes into action, and the transmitting machine
begins to revolve. When the whole of the line print wrapped round the drum
of the machine has passed under the stylus, the end of the shaft D, Fig.
36, engages {97} with the spring _m_, breaking the