causes of accident, as we have shown, has been the structural
weakness of a machine. Now, with the experience of the war on which to
draw, and with many clever brains focussed on the development of the
industry, this risk may be regarded as almost non-existent; as
negligible a factor as it is possible to make it, remembering that
aircraft, like other mechanism, have to be built by human hands.

Another risk, that of engine failure, may, as we have explained, be
eliminated by the use of more than one motor. In the application of
such systems there is still much to be learned; but the obstacles are
not insuperable. One advantage that can be offered the aerial tourist,
reckoning him as a pilot of no more than average skill, who needs all
the aid that science can give him, is that he can obtain a machine
which, owing to its automatic stability, requires merely to be taken
into the air and brought to earth again, and which will practically
fly itself, once it is aloft.

One of the needs with a touring machine, to which makers must devote
their attention, is that it should be able to leave the ground quickly
in its ascent, and so permit its pilot to rise even from a small
starting ground. And it is equally necessary that, on occasion, a
machine should be able to alight safely, and at a slow speed, in quite
a small field. An aviator who had given up aviation temporarily, after
a long spell of cross-country flying, was asked one day when he was
going to fly again. "I shan't do so," he said, "till I can buy a
machine with which I can alight in my own garden."

Already there are craft which, provided high speeds are not expected
of them, and they are given ample plane-surface, will alight at quite
a moderate pace; but in the future, by the use of machines which have
the power of increasing or reducing their wing-surfaces while in
flight, it should be possible to descend in a space no larger, say,
than a garden. In the construction of variable-surface machines,
technical problems need to be faced which are unusually difficult. The
theory with such craft is that their sustaining planes, either by a
telescopic system, or by some process of reefing, are built so that
they can be expanded or contracted at the will of the pilot. Thus in
rising, when a machine is required to ascend with a minimum run
forward across the ground, a large area of lifting surface would be
exposed; and at the moment of alighting, also, when it was desired