326 On Aérial Navigation. 
mixture too nearly the same as atmospheric air to be of any use 
in this instance; but if azote in the ratio of one half, or even 
two to one, be ascertained to be sufficient, it will be an excellewe 
step gained towards realizing this invention. 
It is evident that if aérial navigation ever be brought home 
to the usés of man (and who, noting the progressive stages of 
society, can set a limit to the powers “which the benevolent Au- 
thor of his being designed him by proper gradations to become 
possessed of?), it can only be done upon a scale of which the 
balloon described is the first ,unit ; and althoughsin the present 
day this unit is abundantly large enough in a practical point of 
view to occupy all the attention that can be afforded to the sub- 
ject; yet I shall nevertheless obtrude a little in prospect upon 
the duties of our posterity respecting this art, as in a doing the 
capabilities that remain in store for our race will operate as an 
encouragement towards our availing ourselves of the first step. 
It has already been observed, that as balloons increase in size, the 
diminution of their relative resistance, when compared with their 
power, keeps pace with that increase. Upon this principle it is 
easy to show that a balloon of the form delineated, inflated with 
hydrogen gas, when extended to the length of 144 yards, will 
meet with no more resistance when compared with the weight 
it will sustain, including its materials, than the resistance of the 
bird compared with its weight. Surely we cannot wish for a 
better basis for swift aérial navigation, than that of a vessel ca- 
pable of suspending in the air as many multiples of the weight 
of the bird, as its resistance contains multiples of the resistance 
of the bird at the same velocity. This balloon would require 
11880 square yards of cloth, which would fold within a cubic 
chest rather exceeding four yards each way, if of single struc- 
ture; but I have taken it as a double structure, which would of 
course require two such spaces, and the weight at two pounds 
per yard will be 24000 pounds. I allow 17000 pounds for the 
other materials, including a surface of the necessary extent for 
waftage; when, deducting these weights, the supporting power, 
which is 163,000 pounds, will be reduced to 122,000 pounds, or 
50 tons. This power remains to be divided in a proper ratia 
between the weight of the first mover and that of the cargo or 
crew intended to be conveyed. Although two-thirds of the 
weight of most birds is devoted to the muscles of its wings, and 
arguing from the rapid consumption of ‘their food, that their 
muscles may be more energetic than those of quadrupeds, weight 
for weight 5 yet it is improbable that this excess is in any great 
proportion. The famous race-horse Eclipse is said to have gone 
for one mile at the rate of 60 miles per hou, which is a far 
greater velocity than any bird whose flight I have measured ; a 
AC 
