to make another quick calculation in his range, it merely
rolled once, then dipped twice, and proceeded on its way. The Archie
fire ceased as suddenly as it had commenced.

McGee streaked across another open patch of sky and entered another
cloud. Coming out of this one he again spotted the lone Nieuport and
corrected his own line to correspond with that of the lone flyer below.
Now, studying it more closely, and with more time, he felt sure that it
was Siddons' plane. One thing certain, the red, white and blue cockades
established it as an American manned plane, and who, save a novice,
McGee reasoned, would roll and make a slight dip to escape Archie fire.
That particular battery must have been too convulsed by laughter to
continue their fire. Had that stupid pilot, whoever he was, forgotten
what he had been told concerning Archie fire?

With the same surprising suddenness with which Archies always proclaim
their presence, three more black puff balls inked the air directly ahead
of the Nieuport. They were off the mark, but they furnished data for
other guns which began filling the air. Evidently the gunners had not
yet seen McGee, who was much higher and considerably behind the
Nieuport, for they were concentrating on that plane.

To McGee's surprise the Nieuport again rolled, then dipped twice, and
the guns below immediately ceased firing. McGee decided it was time to
seek the seclusion of a nearby cloud and while driving through it, do a
little thinking.

What he had just witnessed was enough to make any experienced pilot
think. Someone, flying a Nieuport, had a most novel way of treating with
anti-aircraft gunners. He merely rolled over, straightened out, dipped
twice, and the guns promptly left off their quarreling. No one could be
stupid enough to reason that such manoeuver would discomfit the gunners,
and yet in this case the effect was more efficacious than any manoeuver
yet invented.

McGee smiled at the stupidity of the thought. It was effective only
because it was a signal, prearranged and understood by the anti-aircraft
gunners. The pilot of that Nieuport was in communication with the enemy,
and McGee believed that man to be Siddons!

It all came to him in a flash. Who, better than Siddons, could have
supplied the enemy with the information that brought them over to bomb
the green squadron when they were stationed near Is-Sur-Tille? Someone
supplied it, for Cowan had found in the pocket of the German f