the transmitting
end. Scratches are made upon the smoked plate, and these reproduce the
picture on the original plate. A print can be taken from this scratched
plate in a similar manner to an ordinary photographic negative.

The two tables are synchronised in the following manner. Every time the
transmitting table is about to start its forward stroke a powerful spark is
produced at the spark-gap. The waves set up by this spark operate an
ordinary metal filings coherer at the receiving end which completes the
circuit of an electro-magnet. The armature of this magnet on being
attracted immediately releases the motor used for driving, allowing it to
operate the table. The time taken to transmit a photograph, quarter-plate
size, is about fifteen minutes. {12} Although very ingenious this system
would not be practicable, as besides speed the quality of the received
pictures is a great factor, especially where they are required for
reproduction purposes. The results from the above apparatus are said to be
very crude, as with the method used to prepare the photographs no very
small detail could be transmitted.

* * * * *

{13}

CHAPTER II

TRANSMITTING APPARATUS

Let us now consider the requirements necessary for transmitting photographs
by means of the wireless apparatus in use at the present time.

[Illustration: FIG. 4.]

The connections for an experimental syntonic wireless transmitting station
are shown in the diagram Fig. 4. A is the aerial; T, the inductance; E,
earth; L, hot-wire ammeter. The closed oscillatory circuit consists of an
inductance F, spark-gap G, and a block condenser C. H is a spark-coil for
supplying the energy, the secondary J being connected to the spark-gap. A
{14} mercury break N and a battery B are placed in the primary circuit of
the coil. The Morse key K is for completing the battery circuit for
signalling purposes. When the key K is depressed, the battery circuit is
completed, and a spark passes between the balls of the spark-gap G
producing oscillations in the closed circuit, which are transposed to the
aerial circuit by induction. For signalling purposes it is only necessary
for the operator by means of the key K to send out a long or short train of
waves in some pre-arranged order, to enable the operator at the receiving
station to understand the message that is being transmitted.

If a photograph could be prepared in such a manner that it would ser