them. As soon as the local circuit
of the relay is closed, the current from the battery Z (about 12 volts)
flows through the paper and produces a coloured mark. The picture,
therefore, is composed of long or short marks which correspond to the
varying strips of conducting material on the single line print. In order to
render the marks short and crisp, a small battery Y, and regulating
resistance L, is placed across the drum and stylus. The diagram, Fig. 30,
gives the connections for the complete receiver. {56}

The paper used is soaked in a solution consisting of

Ferrocyanide of potassium 1/4 oz.
Ammoniac Nitrate 1/2 oz.
Distilled water[8] 4 oz.

[Illustration: FIG. 30.]

The paper has to be very carefully chosen, as besides being absorbent
enough to remain moist during the whole of the receiving, the surface must
also remain fairly smooth, as with a rough paper the grain shows very
distinctly, and if there is an excess of solution the electrolytic marks
are inclined to spread and so cause a blurred image. The writer tried
numerous specimens of paper before one could be found that gave really
satisfactory results. It was also found that when working in a warm room
the paper became nearly {57} dry before the receiving was finished, and the
resistance of the paper being greatly increased (this may be anything up to
1000 ohms), the marking became very faint. A sponge moistened with the
solution and applied to the undecomposed portion of the paper, while still
revolving, was found to help matters considerably.

Another experience which happened during the writer's early experiments,
the cause of which I am still unable to explain, occurred in connection
with the stylus. The stylus used consisted of a sharply pointed steel
needle, and after working for about three minutes it was noticed that the
lines were becoming gradually wider, finally running into each other. Upon
examination it was found that the point of the needle had worn away
considerably, becoming in fact, almost a chisel point. Almost every needle
tried acted in a similar manner, and to overcome this difficulty the stylus
shown in Fig. 31 was devised.

It will be seen that it consists of a holder A, somewhat resembling a drill
chuck, fastened to the flat spring B in such a manner that the angle the
stylus makes to the drum can be altered. The needle consists of a length of
36-gauge steel wire, an