ayley, and others, had already stated
this, but to Lilienthal belongs the honour of being first to put the
statement to effective proof--he made over 2,000 gliding flights
between 1891 and the regrettable end of his experiments; his practical
conclusions are still regarded as part of the accepted theory of
students of flight. In 1889 he published a work on the subject of
gliding flight which stands as data for investigators, and, on the
conclusions embodied in this work, he began to build his gliders and
practice what he had preached, turning from experiment with models to
wings that he could use.

It was in the summer of 1891 that he built his first glider of rods of
peeled willow, over which was stretched strong cotton fabric; with this,
which had a supporting surface of about 100 square feet, Otto Lilienthal
launched himself in the air from a spring board, making glides which, at
first of only a few feet, gradually lengthened. As his experience of
the supporting qualities of the air progressed he gradually altered
his designs until, when Pilcher visited him in the spring of 1895,
he experimented with a glider, roughly made of peeled willow rods and
cotton fabric, having an area of 150 square feet and weighing half a
hundredweight. By this time Lilienthal had moved from his springboard to
a conical artificial hill which he had had thrown up on level ground at
Grosse Lichterfelde, near Berlin. This hill was made with earth taken
from the excavations incurred in constructing a canal, and had a cave
inside in which Lilienthal stored his machines. Pilcher, in his paper
on 'Gliding,' [*] gives an excellent short summary of Lilienthal's
experiments, from which the following extracts are taken:--

[*] Aeronautical Classes, No. 5. Royal Aeronautical Society's
publications.

'At first Lilienthal used to experiment by jumping off a springboard
with a good run. Then he took to practicing on some hills close to
Berlin. In the summer of 1892 he built a flat-roofed hut on the summit
of a hill, from the top of which he used to jump, trying, of course, to
soar as far as possible before landing.... One of the great dangers with
a soaring machine is losing forward speed, inclining the machine too
much down in front, and coming down head first. Lilienthal was the
first to introduce the system of handling a machine in the air merely
by moving his weight about in the machine; he always rested only on his
elbows or on his elbows and sho