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.
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