But surfaces are as the squares of
the dimensions. The square of two is four. The heavier machine
will therefore expose only four times the wing surface to the air,
and so will have a distinct disadvantage in the ratio of
efficiency to weight.
Mechanical principles show that the steam pressures which the
engines would bear would be the same, and that the larger engine,
though it would have more than four times the horse-power of the
other, would have less than eight times. The larger of the two
machines would therefore be at a disadvantage, which could be
overcome only by reducing the thickness of its parts, especially
of its wings, to that of the other machine. Then we should lose in
strength. It follows that the smaller the machine the greater its
advantage, and the smallest possible flying-machine will be the
first one to be successful.
We see the principle of the cube exemplified in the animal
kingdom. The agile flea, the nimble ant, the swift-footed
greyhound, and the unwieldy elephant form a series of which the
next term would be an animal tottering under its own weight, if
able to stand or move at all. The kingdom of flying animals shows
a similar gradation. The most numerous fliers are little insects,
and the rising series stops with the condor, which, though having
much less weight than a man, is said to fly with difficulty when
gorged with food.
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