erver scan the
line closely for a stationary train, as the Boche engine-drivers usually
try to avoid detection by shutting off steam. The Hun has many other
dodges to avoid publicity. When Allied aircraft appear, motor and horse
transport remain immobile at the roadside or under trees. Artillery and
infantry are packed under cover; though, for that matter, the enemy very
rarely move troops in the daytime, preferring the night or early
morning, when there are no troublesome eyes in the air.

To foil these attempts at concealment is the business of the observers
who gather information for Army Headquarters and G. H.Q. For observers
on corps work the detective problems are somewhat different. This
department deals with hidden saps and battery positions, and draws and
photographs conclusions from clues such as a muzzle-blast, fresh tracks,
or an artificial cluster of trees. All reconnaissance observers must
carry out a simultaneous search of the earth for movement and the sky
for foes, and in addition keep their guns ready for instant use. And
should anything happen to their machines, and a forced landing seem
likely, they must sit tight and carry on so long as there is the
slightest hope of a safe return.

A nos moutons. I made a long list in my note-book of the places where
something useful was likely to be observed, and tried my gun by firing a
few shots into the ground. We hung around, impatient at the long delay.

"Get into your machines," called the Squadron Commander at last, when a
telephone message had reported that the weather conditions toward the
east were no longer unfavourable. We took to the air and set off.

V. led his covey beyond Albert and well south of the Somme before he
turned to the left. Then, with the strong wind behind us, we raced
north-east and crossed the strip of trenches. The pilot of the emergency
machine, which had come thus far to join the party if one of the other
four dropped out, waved his hand in farewell and left for home.

Archie barked at us immediately, but he caused small trouble, as most of
his attention was already claimed by a party of French machines half a
mile ahead. Anyhow we should have shaken him off quickly, for at this
stage of the journey, with a forty-mile wind reinforcing our usual air
speed of about ninety-five miles an hour, our ground speed was
sufficient to avoid lingering in any region made unhealthy by A.-A.
guns. The water-marked ribbon of trenches seemed a