ong
distances, and the extra time and expense required to receive a fairly good
detailed picture is negligible when compared with the enormous time it
would take to receive the original photograph by any ordinary means of
transit.

The public much prefer to have passable pictorial illustrations of current
events than wait several days for a more perfect picture--the original, and
the advantage of any newspaper being able to publish photographs several
days before its rivals is obvious. There can also be no doubt but that a
system of radio-photography, if fairly reliable and capable of working over
a distance of say thirty miles, would be of great military use for
transmitting maps and written matter with a great saving of time and even
life. Written matter could be transmitted with even greater safety than
messages which are sent in the ordinary way in Morse Code, as the signals
received in the receiver {36} of an hostile installation would be but a
meaningless jumble of sounds, and even were they possessed of
radio-photographic apparatus the received message would be unintelligible,
unless they knew the exact speed at which the machines were running and
could synchronise accurately.

* * * * *

{37}

CHAPTER III

RECEIVING APPARATUS

There are only two methods available at present for receiving the
photographs, and both have been used in ordinary photo-telegraphic work
with great success. They have disadvantages when applied to wireless work,
however, but these will no doubt be overcome with future improvements. The
two methods are (1) by means of an ordinary photographic process, and (2)
by means of an electrolytic receiver.

In several photo-telegraphic systems the machine used for transmitting has
the cylinder twice the size of the receiving cylinder, thus making the area
of the received picture one-quarter the area of the picture transmitted.
The extra quality of the received picture does not compensate for the
disadvantage of having to provide two machines at each station, and in the
writer's opinion results, quite good enough for all practical purposes, can
be obtained by using a moderate size cylinder so that one machine answers
for both transmitting {38} and receiving, and using as fine a line screen
as possible for preparing the photographs.

[Illustration: FIG. 18.]

The writer, when first experimenting in photo-telegraphy, endeavoured to
make the receiving apparat