the magnitude of the figures we are here employing, as if it were
something extraordinary or beyond the power of man to accomplish. The
dimensions and power we have here assumed is very little greater than
those of the great Vauxhall Balloon,[A] and considerably less than
some of _Montgolfières_, or Fire-balloons, which were first
employed.

[Footnote A: The height of the Vauxhall Balloon is about eighty feet,
its breadth about fifty. It contains 85000 cubic feet of gas, and
supports a weight of upwards of two tons.]

Now the resistance which such a Balloon as I have here described would
experience in its passage through the air, and consequently the power
it would require to establish that resistance compared with those
of the model, we have said would be as the _squares_ of their
respective diameters, or in, about, the ratio of only fifty-six to
one; in other words, whatever force it would take to propel the model
at any given rate, it would require just fifty-six times the power
to accomplish the same result with the large Balloon we have been
describing.

In order to ascertain precisely what this power would be in any given
instance, it only remains to find an expression for the spring power
with which we have been hitherto dealing, that shall be more generally
comprehensible.

This we shall do by a comparison with the power of steam, according to
the usual mode of estimating it; that is, reckoning a one-horse power
to be equal to the traction or draught of 32,000 lbs. through the
space of one foot in a minute. According to this scale, observing the