tical fin aft, he began his
gliding experiments. His whole apparatus, made of peeled willow sticks,
covered with cotton shirting, weighed less than forty pounds. He was
supported in it wholly on his forearms, which passed through padded
tubes, while his hands grasped a cross-bar. He guided the machine and
preserved its balance by shifting his weight, backwards or forwards or
sideways. In this apparatus, altered and improved from time to time,
Lilienthal, during the next five years, made more than two thousand
successful glides. At first he used to jump off a spring-board; then he
practised on some hills in the suburbs of Berlin; then, in the spring of
1894, he built a conical hill at Gross-Lichterfelde to serve him as a
starting-ground. Later on, he moved to the Rhinow hills. His best glides
were made against a light breeze at a gradient of about 1 in 10; and he
could easily travel a hundred yards through the air. 'Regulating the
centre of gravity', he says, 'becomes a second nature, like balancing on
a bicycle; it is entirely a matter of practice and experience.' His most
alarming experiences were from gusts of wind which would suddenly raise
him many metres in the air and suspend him in a stationary position. But
his skill was so great that he always succeeded in resuming his flight
and alighting safely. He continued to improve and develop his machine.
He made a double-surface glider, on the biplane principle, and flew on
it. He experimented with engines, intended to flap the extremities of
the wings--first a steam-engine of two horse-power, weighing forty-four
pounds, then a simpler and lighter type, worked by compressed carbonic
acid gas. But he explains that these can be safely introduced only if
they do not impair the gliding efficiency of the machine, and he does
not seem to have made much progress with them. His last improvement was
a movable horizontal tail, or elevator, worked by a line attached to his
head, to control the fore-and-aft balance of the machine. This fresh
complexity was perhaps the cause of his death. On the 9th of August 1896
he started on a long glide from a hill about a hundred feet high; a
sudden gust of wind caught him, and it is supposed that the involuntary
movements of his head in the effort to regain his balance made matters
worse; the machine plunged to the ground, and he was fatally injured.

Lilienthal was a good mathematician, a careful recorder of the results
of his experiments, and