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CHAP. III. 



ON THE CAUSE WHICH M AK ES ROCKETS ASCEND INTO 



THE AIR. 



As this cause is nearly the same as that which produces recoil in 

 fire-arms, it is best explained by illustrating the latter. 



When the powder is suddenly inflamed in the chamber, or at the 

 bottom of the barrel, it necessarily exercises an action two ways at 

 the same time ; that is to say, against the breech of the piece, and 

 against the bullet or wadding, which is placed above it. Besides 

 this, it acts also against the sides of the chamber which it occupies ; 

 and as they oppose a resistance almost insurmountable, the whole 

 effort of the elastic fluid, produced by the inflammation, is exerted 

 in the two dirpctions above mentioned. But the resistance opposed 

 by the bullet, being much less than that opposed by the mass of the 

 barrel or cannon, the bullet is forced out with great velocity. It is 

 impossible, however, that the body of the piece itself should not ex- 

 perience a movement backwards ; for if a spring is suddenly let 

 loose, between two moveable obstacles, it will impel them both, 

 and communicate to them velocities in the inverse ratio of their 

 masses ; the piece therefore must acquire a velocity backwards 

 nearly in the inverse ratio of its mass to that of the bullet. We 

 make use of the term nearly, because there are various circum. 

 stances which give to this ratio certain modifications ; but it is 

 always true that the body of the piece is driven backwards, and 

 that if it weighs with its carriage, a thousand times more than 

 the bullet, it acquires a velocity, which is a thousand times less, 

 and which is soon annihilated by the friction of the wheels against 

 the ground, &c. 



The cause of the ascent of the rocket is nearly the same. At the 

 moment when the powder begins to inflame, its expansion produces 

 a torrent of elastic fluid, which acts in every direction; that is, 

 against the air which opposes its escape from the cartridge, and 

 against the upper part of the rocket j but the resistance of the air 

 is more considerable than the weight of the rocket, on account of 



