Now, as a matter of fact, a slight slope of the wings would undoubtedly
produce a raising power, and so an answer is at one obtained to this
objection. But I venture to assert, with the utmost confidence, that a
perfectly horizontal plane, advancing swiftly in a horizontal direction
at first, will not sink as quickly, or anything like as quickly, as a
similar plane let fall from a position of rest. A cannon-ball, rushing
horizontally from the mouth of a cannon, begins to fall just as if it
were simply dropped. But the case of a horizontal plane is altogether
different. If rapidly advancing, it passes continually over still air;
if simply let fall, the air beneath it yields, and presently currents
are set up which facilitate the descent of the flat body; but there is
no time to set up these aerial movements as the flat body passes rapidly
over still air.
As a matter of fact, we know that this difference exists, from
the difference in the observed behavior of a flat card set flying
horizontally through the air and a similar card held horizontally and
then allowed to fall.
I believe the whole mystery of aerial flotation lies here, and that as
soon as aerial floating machines are planned on this system, it will be
found that the problem of aerial transit--though presenting still many
difficulties of detail--is, nevertheless, perfectly soluble.
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