deavouring to
go against it, with the force just ascribed to them, than if they
were to exercise the same force in any other direction, or in a water
perfectly tranquil. Apply this reasoning to the case of a Balloon
propelled by machinery, and much of the obscurity in which it is
involved will disappear.]

With these conditions established, it will now be seen that we have
nothing to consider, in discussing the probable success of any scheme
of aerial navigation with the aid of the Balloon (so far as its mere
movements are concerned)[A] except the _actual rate of motion_
which it is competent to accomplish; whether or not it be sufficient
to meet the exigencies of the case as they may happen to be estimated.
That its capabilities in that respect, be displayed within a room, or
in a calm atmosphere, or under what may be called the most favourable
circumstances, has nothing in it to disparage or affect the general
question. Whatever it can do _there_, it can do the same in a
hurricane; and the only real question is, "whether, what it _can_
accomplish in respect of rate, is enough to answer the purpose in
view."

[Footnote A: I have said "so far as its mere movements are concerned;"
because the complete success of the scheme, how far it is an available
and satisfactory mode of transport, depends upon other conditions
besides the accomplishment of a given rate of motion--as for instance,
whether it be safe, or practicable, or consistent with a due
preservation of the _buoyancy_ of the Balloon, so as to allow of
its being employed in voyages of sufficient distance and duration,
or capable of being worked at moderate cost, or whether it leave
sufficient allowance for cargo; with many others of less striking
importance, which the practical aeronaut will readily suggest for
himself.]

The model we have been just describing is capable as we have seen, of
accomplishing a rate of about six miles an hour. Now the resistance to
the progress of a Balloon varies as the squares of the velocities or
rates of motion. Accordingly, for the same Balloon to accomplish
twice the speed, or twelve miles an hour, it would be necessary to be
provided with four times the power. Thus as the spring power employed
in the model is equal to a weight of 45 pounds, upon a barrel of four
inches in diameter, it would require one competent to raise 180 pounds
on the same sized barrel, to enable it to propel the same Balloon at
double the present rate.