are
obtained, and the machine given the strength indicated, this factor of
safety is insufficient. It is not so much the normal strains, as those
which are abnormal, that must be guarded against in flight. A
high-speed machine, if piloted on a day when the air is turbulent, may
be subjected to extraordinarily heavy strains; rising many feet in the
air one moment, falling again the next, and being met suddenly by
vicious gusts of wind--in much the same way that a fast-moving ship,
when fighting its way through a rough sea, is beaten and buffeted by
the waves. Air waves have not of course the weight, when they deliver
a blow, that lies behind a mass of water; but that these wind-waves
attain sometimes an abnormal speed, and have a tremendous power of
destruction, is shown in the havoc that is caused by hurricanes.

It seems astonishing to many people that such a frail machine as the
aeroplane, with its outspread wings containing nothing stronger often
than wooden spars and ribs, covered by a cotton fabric, should be
capable of being driven through the air at such a speed, say, as 100
miles an hour, encountering not only the pressure of the air, but
resisting also the fluctuations to which it may be subjected. But,
underlying the lightness and apparent frailty of such a wing, when one
sees it in the workshop in its skeleton form, before it has been
clothed in fabric, there is a skill in construction, and an experience
in the choice, selection, and working of woods, that produces a
structure which, for all its fragile appearance, is amazingly strong.
And the same applies, nowadays, to all the other parts of an
aeroplane. That it should have taken years to gain such strength, and
to reduce so largely the risk of breakage, is not in itself
surprising. Men had to devise new methods in construction--always with
the knowledge that weight must be saved--and to create new factors of
safety, before they could build an airworthy craft.

To-day, when a man flies, he need have no lurking fear, as had the
pioneers, that his craft may break in the air. Even when it is driven
through a gale, plunging in the rushes of the wind, yet held straining
to its task by the power of its motor, the modern aeroplane can be
relied upon; and not in one detail of its construction, but in every
part. Experience, the researches of science, and the growing skill
with which aircraft are built, stand between the airman and many of
his previous dangers. Th