n agent down the funnel of a vessel into the boiler-room
is a favourite theme among writers of fiction and artists. But hitting
such an objective while it is tearing at high speed through the water,
from a height of several thousand feet is a vastly different task from
throwing sticks and balls at an Aunt Sally on terra firma: the target is
so small and elusive.

Practically it is impossible to employ the flying machine, whether it
be a dirigible or an aeroplane, in this field. Many factors militate
against such an application. In the first place there is a very wide
difference between dry land and a stretch of water as an area over which
to manoeuvre. So far as the land is concerned descent is practicable at
any time and almost anywhere. But an attempt to descend upon the open
sea even when the latter is as calm as the proverbial mill-pond is
fraught with considerable danger. The air-currents immediately above the
water differ radically from those prevailing above the surface of
the land. Solar radiation also plays a very vital part. In fact the
dirigible dare not venture to make such a landing even if it be provided
with floats. The chances are a thousand to one that the cars will become
water-logged, rendering re-ascent a matter of extreme difficulty, if not
absolutely impossible. On the other hand, the aeroplane when equipped
with floats, is able to alight upon the water, and to rest thereon for
a time. It may even take in a new supply of fuel if the elements be
propitious, and may be able to re-ascend, but the occasions are rare
when such operations can be carried out successfully.

In operations over water the airman is confronted with one serious
danger--the risk of losing his bearings and his way. For instance, many
attempts have been made to cross the North Sea by aeroplane, but only
one has proved successful so far. The intrepid aviator did succeed in
passing from the shore of Britain to the coast of Scandinavia. Many
people suppose that because an airman is equipped with a compass he must
be able to find his way, but this is a fallacy. The aviator is in the
same plight as a mariner who is compelled from circumstances to rely
upon his compass alone, and who is debarred by inclement weather from
deciding his precise position by taking the sun. A ship ploughing the
waters has to contend against the action of cross currents, the speed
of which varies considerably, as well as adverse winds. Unless absolute
correc