d that
the metal print used for {60} transmitting is a positive, since it is
prepared from a negative. The received picture will therefore be a
negative, making the final reproduction, if it is to be used for newspaper
work, a negative also. Obviously this is no good. The final reproduction
must be a positive, therefore the received picture must be also a positive.
To overcome this difficulty matters must be so arranged at the receiving
station that in the cases of Figs. 17, 18, 22, and 24, the film is kept
permanently illuminated while the stylus on the transmitter is tracing over
an insulating strip, and in darkness when tracing over a conducting strip.
In Fig. 30 the relay F should allow a continuous current from Z to flow
through the electrolytic paper, and only broken when the resistance of the
selenium cell is sufficiently reduced to allow the current from D to
operate the relay.

The author has endeavoured to make direct positives on glass of the picture
to be transmitted, so that a negative metal print could be prepared. The
results obtained were not very satisfactory, but the method tried is given,
as it may perhaps be of interest. The plate used in the camera has to be
exposed three or four times longer than is required for an ordinary
negative. The exposed plate is then placed in a solution of protoxalate of
iron (ferrous oxalate) and left until the image shows plainly through the
back of the plate. It {61} is then washed in water and placed in a solution
consisting of

Distilled water 1000 cc.
Nitric acid 2 cc.
Sulphuric acid 3 cc.
Bichromate of potash 105 grammes.
Alum 80 "

After being in this bath for about fifteen minutes the plate is again well
washed in water, and developed in the ordinary way. The first two
operations should be performed in the dark room, but the remaining
operations can be performed in daylight, once the plate has been placed in
the bichromate bath. As already stated, the results obtained were not very
satisfactory, and such a method is not now worth following up, as it is
comparatively easy so to arrange matters at the receiving station that a
positive or negative image can be received at will.

It is necessary to connect the stylus of the receiving machine to the
positive pole of the battery Z, otherwise the marks will be made on the
undersi