Bho J . 
XVII. On Aérial Navigation. By Sir Groner Cayiry, Bart. 
ae 
Toa Mr. Tilloch. 
Sir, — I AM glad to find that the public attention is ¢alled to 
aérial navigation by Mr. Evans, in your Magazine for November 
% last. This subject is of great importance to mankind, ‘and is 
worthy of more attention than is bestowed upon it. An unin- 
terrupted navigable ocean, that comes to the threshold of every 
man’s door, ought not to be neglected as a source of human 
; gratification and advantage. Mr. Evans proposes the action of 
i a large inclined plane suspended below a common balloon, as 
’ the means of making it take an oblique course in its ascent, and 
; -by means of the same plane to make the weight of the appa- 
. ratus cause an oblique descent towards the same point of steer- 
age. This principle is unquestionably capable of performing 
what that gentleman proposes, although the construction he has 
given is only adapted to effect the purpose in ascending, as the 
want of weight in the plane would prevent it from operating, 
excepting in a very limited degree, in the descent. In the small 
balloons used by Mr. Evans, the plane was, in fact, the whole 
burthen supported; and hence, under the small velocity gene- 
rated, the descent was as oblique as the ascent. But in the 
balloon 80 feet in diameter described by that gentleman, the 
plane in ascending would receive, according to his estimate, 
above 2000 pounds of resistance from the an’, and thus become 
efficient ; whereas in descending it could only sustain a resist- 
ance equal to its weight, which of course will be as little as pos- 
sible, and hence it will be nearly inefficient. The general prin- 
ciple, however, is perfectly true; and when applied advantageously, 
although it is an indirect way of gaining the proposed horizontak 
point, yet it will be as effectual as the process of tacking in or- 
dinary navigation. Mr. Evans estimates that a Montgolfier 
balloon of 80 feet in diameter, with a plane suspended under it 
in an angle of 70° with a perpendicular line, the dimensions of 
which are as 1:4 to 1, compared with the great circle of the 
balloon, will be carried through the air by a power of ascent 
equal to 2792 pounds with a velocity of 28 feet per second, and 
hence that the travelling horizontal speed will be about 19 miles 
per hour.—If the resistance of air be taken at one pound per 
square foot at a velocity of 23 feet per second, which is two feet 
more than the common engineering estimate, the resistance of 
a globe to its great circle, according to Mr. Robins’s experi-, 
ments, as 1 to 2°27, and the resistance of the plane as the square 
Vol, 47, No, 214. Feb. 1816. F of 
