sition, thereby enabling the observers to complete
their task carefully and with deliberation.

On the other hand, the means of enabling an aeroplane to hover still
remain to be discovered. It must travel at a certain speed through the
air to maintain its dynamic equilibrium, and this speed is often too
high to enable the airman to complete his reconnaissance with sufficient
accuracy to be of value to the forces below. All that the aeroplane can
do is to circle above a certain position until the observer is satisfied
with the data he has collected.

But hovering on the part of the dirigible is not without conspicuous
drawbacks. The work of observation cannot be conducted with any degree
of accuracy at an excessive altitude. Experience has proved that the
range of the latest types of anti-aircraft weapons is in excess of
anticipations. The result is that the airship is useless when hovering
beyond the zone of fire. The atmospheric haze, even in the clearest
weather, obstructs the observer's vision. The caprices of this obstacle
are extraordinary, as anyone who has indulged in ballooning knows fully
well. On a clear summer's day I have been able to see the ground beneath
with perfect distinctness from a height of 4,500 feet, yet when the
craft had ascended a further two or three hundred feet, the panorama was
blurred. A film of haze lies between the balloon and the ground beneath.
And the character of this haze is continually changing, so that the
aerial observer's task is rendered additionally difficult. Its effects
are particularly notice able when one attempts to photograph the view
unfolded below. Plate after plate may be exposed and nothing will be
revealed. Yet at a slightly lower altitude the plates may be exposed and
perfectly sharp and well-defined images will be obtained.

Seeing that the photographic eye is keener and more searching than the
human organ of sight, it is obvious that this haze constitutes a very
formidable obstacle. German military observers, who have accompanied
the Zeppelins and Parsevals on numerous aerial journeys under varying
conditions of weather, have repeatedly drawn attention to this factor
and its caprices, and have not hesitated to venture the opinion that it
would interfere seriously with military aerial reconnaissances, and also
that it would tend to render such work extremely hazardous at times.

When these conditions prevail the dirigible must carry out its work upon
the broad