CANNON (continued)

The length of any cannon is always reckoned from the hind part of the base ring, or beginning of the cascabel, to the extremity of the muzzle. The second reinforce begins at the same circle where the first terminates; and the chase at the same circle where the second reinforce ends.

The first reinforce therefore includes the base ring; the ogee nearest thereto; the vent-field; the vent-astragal, and first reinforce-ring. The second reinforce contains the ogee next to the first reinforce-ring and the second reinforce-ring. The chase comprehends the ogee nearest to the second reinforce-ring; the chase-girdle and astragal; and the muzzle and astragal. The trunnions are always placed on the second reinforce, so as that the breech-part of the cannon may weigh something more than the muzzle-part, to prevent the piece from starting up behind when it is fired.

A variety of experiments, made with great care and accuracy, prove that powder when on fire possesses at least 4000 times more space than when in grains (Mr. Bigot de Morogues says from 4000 to 4500, and Mr. Haukbee 5000. Therefore if we suppose that the quantity of powder with which a cannon is charged possesses one-fourth of a cubical foot in grains, it will, when on fire, occupy the space of about 1000 cubical feet. The same experiments evince also that the powder, when inflamed, is dilated equally round it's center. One grain of powder fired in the center of different concentric circles, round which grains of powder are placed, shall therefore set fire to all those grains at once.

From this principle it necessarily follows, that powder, when fired in a cannon, makes at the same instant an equal effort on every part of the inside of the piece, in order to expand itself about it's center every way. But as the resistance from the sides of the piece turns the action of the powder, so as to follow the direction of the bore of the cannon, when it presses upon the ball, so as to force it outwards, it presses also on the breech of the cannon; and this gives the piece a motion backwards, that is called it's recoil, which, as we have already observed, is restrained by the breeching and the convexity of the decks. The recoil in some degree diminishes the action of the powder upon the shot. But this cannot be avoided; for, if the carriages were fixed so as not to give way to this motion, the action of the powder, or the effort that causes the recoil, would tear them to pieces in a very short time.

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