s or so in width, but this is a fallacy. The fighting
zone is at least 20 miles in width; that is to say, the occupied
territory in which vital movements take place represents a distance of
20 miles from the foremost line of trenches to the extreme rear, and
then comes the secondary zone, which may be a further 10 miles or
more in depth. Consequently the airman must fly at least 30 miles in
a bee-line to cover the transverse belt of the enemy's field of
operations. Upon the German and Russian sides this zone is of far
greater depth, ranging up to 50 miles or so in width. In these
circumstances the difficulties of ethereal communication 'twixt air and
earth may be realised under the present limitations of radius from which
it is possible to transmit.

But there are reasons still more cogent to explain why wireless
telegraphy has not been used upon a more extensive scale during the
present campaign. Wireless communication is not secretive. In other
words, its messages may be picked up by friend and foe alike with
equal facility. True, the messages are sent in code, which may be
unintelligible to the enemy. In this event the opponent endeavours to
render the communications undecipherable to one and all by what is known
as "jambing." That is to say, he sends out an aimless string of
signals for the purpose of confusing senders and receivers, and this
is continued without cessation and at a rapid rate. The result is that
messages become blurred and undecipherable.

But there is another danger attending the use of wireless upon the
battlefield. The fact that the stations are of limited range is well
known to the opposing forces, and they are equally well aware of the
fact that aerial craft cannot communicate over long distances. For
instance, A sends his airmen aloft and conversation begins between the
clouds and the ground. Presently the receivers of B begin to record
faint signals. They fluctuate in intensity, but within a few seconds B
gathers that an aeroplane is aloft and communicating with its base. By
the aid of the field telephone B gets into touch with his whole string
of wireless stations and orders a keen look-out and a listening ear to
ascertain whether they have heard the same signals. Some report that the
signals are quite distinct and growing louder, while others declare that
the signals are growing fainter and intermittent. In this manner B is
able to deduce in which direction the aeroplane is flying. Thus if