and the wings not too large, or the wind will soon show that
it is not to be trifled with." The inventor commenced with all due
caution, making his first attempt over a grass plot from a spring board
one metre high, and subsequently increasing this height to two and a
half metres, from which elevation he could safely cross the entire grass
plot. Later he launched himself from the lower ridges of a hill 250 feet
high, when he sailed to a distance of over 250 yards, and this time he
writes enthusiastically of his self-taught accomplishment:--

"To those who, from a modest beginning and with gradually increased
extent and elevation of flight have gained full control over the
apparatus, it is not in the least dangerous to cross deep and broad
ravines. It is a difficult task to convey to one who has never enjoyed
aerial flight a clear perception of the exhilarating pleasure of this
elastic motion. The elevation above the ground loses its terrors,
because we have learned by experience what sure dependence may be placed
upon the buoyancy of the air."

As a commentary to the above we extract the following:--"We have to
record the death of Otto Lilienthal, whose soaring machine, during a
gliding flight, suddenly tilted over at a height of about 60 feet,
by which mishap he met an untimely death on August 9th, 1896." Mr. O.
Chanute, C.E. of Chicago, took up the study of gliding flight at the
point where Lilienthal left it, and, later, Professor Fitzgerald
and others. Besides that invented by Penaud, other aero-plane models
demanding mention had been produced by Tatin, Moy, Stringfellow,
and Lawrence Hargrave, of Australia, the subsequent inventor of the
well-known cellular kite. These models, for the most part, aim at the
mechanical solution of the problem connected with the soaring flight of
a bird.

The theoretical solution of the same problem had been attacked by
Professor Langley in a masterly monograph, entitled "The Internal Work
of the Wind." By painstaking experiment with delicate instruments,
specially constructed, the Professor shows that wind in general, so
far from being, as was commonly assumed, mere air put in motion with
an approximately uniform velocity in the same strata, is, in reality,
variable and irregular in its movements beyond anything which had been
anticipated, being made up, in fact, of a succession of brief pulsations
in different directions, and of great complexity. These pulsations, he
argues, if o