The weight of the projectile is 88 pounds, and its remanent velocity at
the moment of impact is 1,295 feet. Under this enormous live force, the
masonry gradually crumbles, and carries along the earth of the parapet,
and opens a breach for the assaulting columns.

[Illustration: FIG. 4--STATE OF A CUPOLA AFTER THE ACTION OF
THIRTY-SEVEN 6 IN. PROJECTILES.]

In order to protect the masonry of the scarp, engineers first lowered
the cordon to the level of the covert-way. Under these circumstances,
the enemy, although he could no longer see it, reached it by a curved or
"plunging" shot. When, in fact, for a given distance we load a gun with
the heaviest charge that it will stand, the trajectory, AMB (Fig. 2), is
as depressed as possible, and the angles, a and a', at the start and
arrival are small, and we have a direct shot. If we raise the chase of
the piece, the projectile will describe a curve in space which would be
a perfect parabola were it not for the resistance of the air, and the
summit of such curve will rise in proportion as the angle so increases.
So long as the falling angle, a, remains less than 45°, we shall have a
curved shot. When the angle exceeds this, the shot is called "vertical."
If we preserve the same charge, the parabolic curve in rising will meet
the horizontal plane at a greater distance off. This is, as well known,
the process employed for reaching more and more distant objects.

[Illustration: Fig. 5.--STATE OF A CAST-IRON CUPOLA AFTER THE BREAKAGE
OF A VOUSSOIR.]

The length of a gun depends upon the maximum charge burned in it, since
the combustion must be complete when the projectile reaches the open
air. It results from this that although guns of great length are capable