discovered except by cutting through the weld, which, of course,
involves a test to destruction. Written, as it has been, in
August, 1920, it is impossible in this chapter to give any
conception of how the developments of War will be applied to
commercial aeroplanes, as few truly commercial machines have yet
been designed, and even those still show distinct traces of the
survival of war mentality. When, however, the inevitable
recasting of ideas arrives, it will become evident, whatever the
apparent modification in the relative importance of different
aspects of design, that enormous advances were made under the
impetus of War which have left an indelible mark on progress.

We have, during the seventeen years since aeroplanes first took
the air, seen them grow from tentative experimental structures
of unknown and unknowable performance to highly scientific
products, of which not only the performances (in speed,
load-carrying capacity, and climb) are known, but of which the
precise strength and degree of stability can be forecast with
some accuracy on the drawing board. For the rest, with the
future lies--apart from some revolutionary change in fundamental
design--the steady development of a now well-tried and well-found
engineering structure.



PART III

AEROSTATICS

I. BEGINNINGS