84 On Atrial Navigation. 
shape by light poles attached to it, and internal cross bracings 
of wire or cord, opposing the tendency to become circular from 
the internal pressure of the heated air: this vessel to be 15 
yards in elevation, 380 in width, and 100 in length, About 
27 yards below this vessel must be suspended a convenient boat- 
shaped car, by six ropes collecting the eordage of the netting. 
This boat must be furnished witha light fire-grate; and an 
oval chimney of thin metal must descend from the balloon and 
cover the fire. This chimney to be furnished with three fine 
wire nets to prevent sparks from passing up it. A sail or rud= — 
der D must be attached to the boat from behind, which can be 
turned to either side by bracing the boom to which it is fixed. 
The cloth made use of being woollen will not be subject to take 
fire; but it is requisite that it should be made air-tight, and like- 
wise impervious to rain, by some coats of paint or varnish on 
the outside. The machine being thus completed so far as it is 
mecessary to try the principle of the znclined plane, as soon as 
the balloon is inflated, let the front ropes be lengthened and the 
hinder ones shortened, till it stands in an angle of about 30° with 
the horizon, when it will be found to rise in an angle of about 45°, 
and the horizontal velocity towards its destined harbour will be 
about 20 miles per hour*.—The power of the heated air would 
be about 17600 pounds: of this about 6800 pounds would be re- 
quired to generate the velocity specified, and the remainder will 
be consumed in the weight of materials, fuel, passengers, &c. 
It may seem at the first view extraordinary that I should 
propose to make use of so long a chimney; and this requires 
some explanation. ‘The exterior resistance of the air to the an- 
terior portion of the balloon, will amount on some parts of it to 
about 26 pounds per square yard at the proposed speed; and 
hence an internal pressure at least equal to this must be created, 
for the purpose of preserving the form of the balloon. This is 
most readily effected by force of the long column of heated air 
passing up such a chimney as I have described; for, were the 
air within it no hotter than the general temperature of the bal- 
loon, the 27 yards of chimney added to half the height of the 
balloon would create a pressure rather exceeding what is re~ 
quired ; and I conceive it will, from its greater rarefaction, cre- 
* This calculation is grounded upon the following data:—That in Mont- 
golfier balloous one cubic yard of space has been found to give 11 ounces 
of power—that the form of the vessel will prevent it from receiving more 
than a third part of the resistance that its greatest cross section would re-= 
ceive at the same velocity ; and that a velocity of twenty-three feet per 
second in air, creates a resistance of one pound per square foot, according 
to some careful experiments of iy own upon a very large scale, 
ate 
