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.

Now, suppose that an inventor succeeds, as well he may, in making a
machine which would go into a watch-case, yet complete in all its
parts, able to fly around the room. It may carry a button, but nothing
heavier. Elated by his success, he makes one on the same model twice as
large in every dimension. The parts of the first, which are one inch in
length, he increases to two inches. Every part is twice as long, twice
as broad, and twice as thick. The result is that his machine is eight
times as heavy as before. But the sustaining surface is only four times
as great. As compared with the smaller machine, its ratio of
effectiveness is reduced to one-half. It may carry two or three
buttons, but will not carry over four, because the total weight,
machine plus buttons, can only be quadrupled, and if he more than
quadruples the weight of the machine, he must less than quadruple that
of the load. How many such enlargements must he make before his machine
will cease to sustain itself, before it will fall as an inert mass when
we seek to make it fly through the air? Is there any size at which it
will be able to support a human being? We may well hesitate before we
answer this question in the affirmative.

Dr. Graham Bell, with a cheery optimism very pleasant to contemplate,
has pointed out that the law I have just cited may be evaded by not
making a larger machine on the same model, but changing the latter in a
way tantamount to increasing the number of small machines. This is
quite true, and I wish it understood that, in laying down the law I
have cited, I limit it to two machines of different sizes on the same
model throughout. Quite likely the most effective flying-machine would
be one carri