streams and railways must be noted--in short
he must obtain an eye photograph of the country he observes and grasp
exactly what is happening there. In winter, with the thermometer well
down, a blood-freezing wind blowing, wreaths of clouds drifting below
and obscuring vision for minutes at a time, the rain possibly pelting
down as if presaging a second deluge, the plight of the vigilant human
eye aloft is far from enviable.

Upon the return of the machine to its base, the report must be prepared
without delay. The picture recorded by the eye has to be set down
clearly and intelligibly with the utmost speed. The requisite
indications must be made accurately upon the map. Nothing of importance
must be omitted: the most trivial detail is often of vital importance.

A facile pencil is of inestimable value in such operations. While
aloft the observer does not trust to his memory or his eye picture, but
commits the essential factors to paper in the form of a code, or what
may perhaps be described more accurately as a shorthand pictorial
interpretation of the things he has witnessed. To the man in the street
such a record would be unintelligible, but it is pregnant with meaning,
and when worked out for the guidance of the superior officers is a mass
of invaluable detail.

At times it so happens that the airman has not been able to complete
his duty within the time anticipated by those below. But he has gathered
certain information which he wishes to communicate without coming to
earth. Such data may be dropped from the clouds in the form of maps or
messages. Although wireless telegraphy is available for this purpose,
it suffers from certain drawbacks. If the enemy possesses an equipment
which is within range of that of the air-craft and the force to which
it belongs, communications may be nullified by the enemy throwing out
a continuous stream of useless signals which "jamb" the intelligence of
their opponents.

If a message--written in code--or a map is to be dropped from aloft it
is enclosed within a special metallic cylinder, fitted with a vane tail
to ensure direction of flight when launched, and with a detonating head.
This is dropped overboard. When it strikes the ground the detonator
fires a charge which emits a report without damaging the message
container, and at the same time fires a combustible charge emitting
considerable smoke. The noise attracts anyone in the vicinity of the
spot where the message has fallen,