oviding both
vertical and horizontal rudders in order to admit of side steering
as well as the control of ascent and descent, and for preserving
equilibrium. He may be said to have anticipated the work of Lilienthal
and Pilcher, since he constructed and experimented with a fixed surface
glider. 'It was beautiful,' he wrote concerning this, 'to see this noble
white bird sailing majestically from the top of a hill to any given
point of the plain below it with perfect steadiness and safety,
according to the set of its rudder, merely by its own weight, descending
at an angle of about eight degrees with the horizon.'

It is said that he once persuaded his gardener to trust himself in this
glider for a flight, but if Cayley himself ventured a flight in it he
has left no record of the fact. The following extract from his work,
Aerial Navigation, affords an instance of the thoroughness of his
investigations, and the concluding paragraph also shows his faith in the
ultimate triumph of mankind in the matter of aerial flight:--

'The act of flying requires less exertion than from the appearance is
supposed. Not having sufficient data to ascertain the exact degree of
propelling power exerted by birds in the act of flying, it is uncertain
what degree of energy may be required in this respect for vessels of
aerial navigation; yet when we consider the many hundreds of miles of
continued flight exerted by birds of passage, the idea of its being only
a small effort is greatly corroborated. To apply the power of the first
mover to the greatest advantage in producing this effect is a very
material point. The mode universally adopted by Nature is the oblique
waft of the wing. We have only to choose between the direct beat
overtaking the velocity of the current, like the oar of a boat, or
one applied like the wing, in some assigned degree of obliquity to it.
Suppose 35 feet per second to be the velocity of an aerial vehicle, the
oar must be moved with this speed previous to its being able to receive
any resistance; then if it be only required to obtain a pressure of
one-tenth of a lb. upon each square foot it must exceed the velocity of
the current 7.3 feet per second. Hence its whole velocity must be 42.5
feet per second. Should the same surface be wafted downward like a wing
with the hinder edge inclined upward in an angle of about 50 deg. 40
feet to the current it will overtake it at a velocity of 3.5 feet per
second; and as a slight un