On Aerial Navigation. 85 
ate as much pressure as will permit the prow of the balloon to 
be depressed to an angle of 30? with the horizon, and still en- 
able it to resist the impression of the air in descending. — It is 
scarcely necessary to observe that the balloon must be, as usual, 
furnished with a large valve at the top, and likewise with one at 
the bottom, to permit the escape of the hottest or coldest air as 
reyuired. If the specific heat of air be to that of water as 1°79 
to I, it will require about 880 pounds of fuel to inflate this bal- 
loon, exclusive of what will be consumed to supply the waste of 
heat during the operation; and when a second rise is required, 
by having suffered the escape of air equal to the power of 6800 
pounds, it will require the rapid combustion of 840 pounds of 
shavings, chopped straw, &c. to create a renewed ascent. Hence, 
including waste, probably about 100 pounds of fuel will be ex- 
pended for every mile of conveyance, exclusive of the first in- 
flation. 
When this experiment has been made, it will be easy to try 
whether the balloon can be driven directly forward hy sails wafted 
by the steam-engine at a less expense of fuel. In the former 
case the balloon had to proceed along two sides of a right-an- 
gled triangle only to gain the length of the hypothenuse : hence, 
as the resistance varies as the square of the velocity, the same 
horizontal speed of conveyance will be obtained with rather less 
than half the resistance in the one case than the other, The 
consumption of a steam horse power is about 30 pounds of wa- 
ter and six or seven pounds of fuel per hour. I have made se- 
veral calculations relative to this subject, but it will occupy too 
much space for any one number of your valuable Magazine to 
detail them ; I shall therefore close this paper, already perhaps 
too long, by stating, that if the dread of fire should deter any 
one from wishing to promote this experiment, notwithstanding 
the adoption of woollen cloth to prevent it, a perfect security 
from this accident may be obtained by using steam in lieu of 
heated air for inflating the balleon, or at least a great mixture 
of it with the heated air. The power of steam is greater than 
air at the usual temperature in Montgolfier balloons in the ratio 
of 18 to 11, although the first inflation will cost more fuel in 
the ratio of 2:6 tol. The resistance to a steam-balloon will be 
only as | to 1-38, when compared with one of the same power 
inflated by heated air; and hence a considerable saving of power 
would be the result of adopting it. But several inconveniences 
arise upon the introduction of steam into balloons, the chief of 
__ which are the necessity of doubling the structure, so as to sus-, 
pend the steam balloon within one of heated air or gas, and of 
the materials being incapable of absorbing water. However, T 
think 
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