building that had been so demolished by shell fire that it seemed
nothing could now inhabit it. But the truth was soon apparent. The
machine gun nest was in the cellar, and from there, well hidden, had
been doing terrible execution on the allied forces. Pausing only to
make sure of his surmise, Tom began to tap out on his wireless key
the location of the hidden machine gun nest.

Most of the aeroplanes carry a wireless outfit. An aerial trails
after them, and the electric impulses, dripping off this, so to
speak, reach the battery headquarters. Owing to the noise caused by
the motor of the airship, no message can be sent to the airman in
return, and he has to depend on signs made on the ground, arrows or
circles in white by day and lighted signals at night, to make sure
that his messages are being received and understood.

The Allies, of course, possess maps of every sector of the enemy's
front, so that by reference to these maps the aircraft observer can
send back word as to almost the precise location of the battery
which it is desired to destroy.

Quickly tapping out word where the battery was located, Tom awaited
developments, circling around the spot in his machine. He was fired
at from guns on the ground below, but, to his delight, no hostile
planes rose to give him combat. A glance across the expanse,
however, showed that Jack was engaging two.

"He's keeping them from me!" thought Tom, and his heart was heavy,
for he realized that Jack might be killed. However, it was the
fortune of war. As long as the Hun planes were fighting Jack they
would not molest him, and he might have time to send word to the