ut having moved a yard, the
whole of the flimsy structure parted in the middle, and the machine
settled down ignominiously upon the ground, its back broken, and with
the discomfited inventor struggling in the _debris_.

It was far from easy, in the early days, for even an expert
constructor to calculate the strains encountered under various
conditions of flight. In wind pressure, under certain states of the
air, there are dangerous fluctuations--fluctuations which, even with
the knowledge we possess to-day, and this is far from meagre, exhibit
phenomena concerning which much more information is required. Machines
have collapsed suddenly, while flying on a day when the wind has been
uncertain, and have done so in a way which has suggested that they had
encountered, suddenly, a gust of an altogether abnormal strength.
Occasionally, though research work in this field is extremely
difficult, it has been possible to gain data as to the existence of
conditions, prevalent as a rule over a small area, which would spell
grave risk for any aeroplane which encountered them. There is a
strange case, verified beyond question, which occurred during some
tests with man-lifting kites at Farnborough. These kites are strongly
built, and withstand as a rule extremely high winds. On this
particular day a kite, when it had reached a certain altitude, was
seen to crumple up suddenly. The wind did not seem specially
strong--not at any rate on the ground; and there appeared no reason
for the breakage of the kite. Another was sent up; but the same thing
happened, and at the same altitude. Then the officer who was in charge
of the kites sent for a superior. A third kite was flown to see what
would happen. This one broke exactly as the others had done, and at
just the same height--about five hundred feet. Precise data could not
be gained as to this phenomenon; but the breaking of these
kites--which had withstood extremely high pressure in previous
tests--was reckoned to be due to the fact that, when they reached a
certain point in the air, they were subjected to the violent strain of
a sudden and complete change in the direction of the wind. To the
pilot of an aeroplane, entering without warning some such area of
danger, the result might naturally be serious in the extreme.

The air has been, and is still, an uncharted sea. It does not flow
with uniformity over the surface of the earth. It is a constantly
disturbed element, and one that has the