movement of the extended surface or plane, as is the case with
the wings of birds, I apply suitable paddle-wheels or other
proper mechanical propellers worked by a steam or other
sufficiently light engine, and thus obtain the requisite power
for onward movement to the plane or extended surface; and in
order to give control as to the upward and downward direction of
such a machine I apply a tail to the extended surface which is
capable of being inclined or raised, so that when the power is
acting to propel the machine, by inclining the tail upwards,
the resistance offered by the air will cause the machine to rise
on the air; and, on the contrary, when the inclination of the
tail is reversed, the machine will immediately be propelled
downwards, and pass through a plane more or less inclined to the
horizon as the inclination of the tail is greater or less; and
in order to guide the machine as to the lateral direction which
it shall take, I apply a vertical rudder or second tail, and,
according as the same is inclined in one direction or the other,
so will be the direction of the machine.'

The machine in question was very large, and differed very little
from the modern monoplane; the materials were to be spars of
bamboo and hollow wood, with diagonal wire bracing. The surface
of the planes was to amount to 4,500 square feet, and the tail,
triangular in form (here modern practice diverges) was to be
1,500 square feet. The inventor estimated that there would be a
sustaining power of half a pound per square foot, and the
driving power was to be supplied by a steam engine of 25 to 30
horse-power, driving two six-bladed propellers. Henson was
largely dependent on Stringfellow for many details of his
design, more especially with regard to the construction of the