ch let
loose by the exploding gases.

Though they were fired at viciously, neither Jack nor his companion was
hit, and they continued on their way, keeping at a good height, as did
their associates, until they were well over the front German lines.

Jack noticed that some of the other planes were dropping lower, to give
their observers a chance to do their work, and, in response to a shove
in his back from the powerful field glasses carried by Harris, Jack sent
his machine down to about the nine-thousand-foot level. By a glance at
the map he could see that they were now over the territory concerning
which a report was wanted.

They were now under a heavy fire from the German anti-aircraft guns, but
Jack was too old a hand to let this needlessly worry him. He sent his
machine slipping from side to side, holding it on a level keel now and
then, to enable Harris to get the photographs he wanted. In addition,
the observer was also making a hasty, rough, but serviceable map of what
he saw.

Jack glanced down, and noted a German supply train puffing its way along
toward some depot, and he headed toward this to give Harris a chance to
note whether there were any supplies of ammunition, or anything else,
that might profitably be bombed later. He also saw several columns of
German infantry on the march, but as they were not out to make an attack
now, they had to watch the Huns moving up to the front line trenches,
there later, doubtless, to give battle.

Back and forth over the German lines flew Jack, Harris meanwhile doing
important observation work. As Jack went lower he came under a fiercer
fire of the batteries, until, it became so hot, from the shrapnel
bursts, that he fain would have turned and made for home. But orders
were orders, and Harris had not yet indicated that he had enough.

Twisting and turning, to make as poor a mark as possible for the enemy
guns, Jack sent his machine here and there. The other pilots were doing
the same. Machine guns were now opening up on them, and once the burst
of fire came so close that Jack began to "zoom." That is he sent his
craft up and down sharply, like the curves and bumps in a roller-coaster
railway track.

By this time the leading plane gave the signal for the return, and,
thankful enough that they had not been hit, Jack swung about. But the
danger was not over. They had yet to pass across the enemy's front line
trenches, and when Harris signaled Jack to go down low in c