the idea of the plane surface so driven as to take advantage of
the resistance offered by the air, and Henson, who as early as
1840 was experimenting with model gliders and light steam
engines, evolved and patented an idea for something very nearly
resembling the monoplane of the early twentieth century. His
patent, No. 9478, of the year 1842 explains the principle of the
machine as follows:--

In order that the description hereafter given be rendered clear,
I will first shortly explain the principle on which the machine
is constructed. If any light and flat or nearly flat article be
projected or thrown edgewise in a slightly inclined position,
the same will rise on the air till the force exerted is
expended, when the article so thrown or projected will descend;
and it will readily be conceived that, if the article so
projected or thrown possessed in itself a continuous power or
force equal to that used in throwing or projecting it, the
article would continue to ascend so long as the forward part of
the surface was upwards in respect to the hinder part, and that
such article, when the power was stopped, or when the
inclination was reversed, would descend by gravity aided by the
force of the power contained in the article, if the power be
continued, thus imitating the flight of a bird.

Now, the first part of my invention consists of an apparatus so
constructed as to offer a very extended surface or plane of a
light yet strong construction, which will have the same relation
to the general machine which the extended wings of a bird have
to the body when a bird is skimming in the air; but in place of
the movement or power for onward progress being obtained by