f approaching under
cover of night or during thick weather, it will metaphorically "hug the
ground." To attempt to complete its task at a great height is to court
failure, as the range of vision is necessarily so limited.

Under these circumstances the mining of the air could be carried out
upon the obvious approaches to a threatened area. The mines, comprising
large charges of high-explosive and combustible material, would be
attached to small captive balloons similar to the "sounding balloons"
which are so much used by meteorologists in operations for sounding the
upper strata of the atmosphere. These pilot balloons would be captive,
their thin wires being wound upon winches planted at close intervals
along the coast-line. The balloon-mines themselves would be sent to
varying heights, ranging from 1,000 to 5,000 feet, and with several
attached to each cable, the disposition of the mines in the air in
such an irregular manner being in fact closely similar to the practice
adopted in the mining of a channel for protection against submarines and
hostile ships.

The suggestion is that these mines should be sent aloft at dusk or upon
the approach of thick and foggy weather, and should be wound in at dawn
or when the atmosphere cleared, inasmuch as in fine weather the floating
aerial menace would be readily detected by the pilot of a dirigible, and
would be carefully avoided. If the network were sufficiently intricate
it would not be easy for an airship travelling at night or in foggy
weather to steer clear of danger, for the wires holding the balloons
captive would be difficult to distinguish.

The mines would depend upon detonators to complete their work, and here
again they would bear a close resemblance to sea-mines. By looping the
mines their deadliness could be increased. The unsuspicious airship,
advancing under cover of darkness or thick weather, might foul one of
the wires, and, driving forward, would tend to pull one or more mines
against itself. Under the force of the impact, no matter how gentle, or
slight, one or more of the detonating levers would be moved, causing the
mine to explode, thus bursting the lifting bag of the vessel, and firing
its gaseous contents. An alternative method, especially when a cable
carried only a single mine, would be to wind in the captive balloon
directly the wire was fouled by an invading aerial craft, the process
being continued until the mine was brought against the vessel and