and stopping the machine. The machine is connected to the driving gear by
the flexible coupling A.

[Illustration: FIG. 35.

M, motor; Y, isochroniser; F, clutch; A, machine; R, stylus; S, relay; X,
gearing; O, circuit breaker; T, receiver; C, condenser; U, telephone relay;
K, polarised relay; L, contact breaker; D, D^1, D^2, D^3, batteries; P,
friction brake; B, B^1, double-pole two-way switches; N, N^1, N^2, single
switches; W, key; E, electric clock; J, telephones.]

The drum measures 5 inches long by 2-1/8 inches diameter, and this takes a
metal print 5 inches by 7 inches, which allows for a lap of about 1/4 inch.
In working, the print is wrapped tightly round the drum, being secured by
means of a little seccotine smeared along one edge. Care must be taken that
the edge of the lap draws away from the point of {78} the stylus and not
towards it. A margin of bare foil, about 1/8 inch wide, should be left on
the print at the commencing edge, the purpose of which will be explained
later.

[Illustration: FIG. 36.]

_The Stylus._--As the drum of the machine travels laterally, by reason of
the threaded shaft and bearing, the stylus must necessarily be a fixture.
It consists of a holder B, drilled to take a hardened steel point S,
attached to the spring M. The spring is arranged to work in the guide F,
which is provided with an adjusting screw W for regulating the pressure of
the stylus upon the print; the pressure being sufficient to enable good
contact to be made, but must not be heavy enough to scratch the soft foil.
The needle should present an angle of about 60deg to the surface of the
print, as this angle has been found to give the best results in working.

To eliminate any sparking that may take place at the point of make and
break, due to the self-induction of the relay coils, a condenser C, about 1
microfarad capacity, should be connected across {79} the drum and stylus.
The complete stylus is given in the drawings, Figs. 37, 37_a_, and also in
the diagrams Figs. 8 and 9.

[Illustration: FIG. 37.

Showing the arrangement for sliding the stylus to or from the machine.]

[Illustration: FIG. 37a.]

_The Relay._--As will be seen from the diagram, Fig. 38, this consists of
two electro-magnets having very soft iron cores, the magnet M being wound
in the usual manner, while the magnet N is wound differentially. The
armature A is made as light as possible, and is pivoted at P, and when
there is no current flowin