The weight of the gun is balanced
by a system of counterpoises and the chains, l, and the breech
terminates in a hollow screw, f, and a nut, g, held between two
directing sectors, h. The cupola is revolved by simply acting upon the
rollers.

[Illustration: FIG. 9.--THE SCHUMANN-GRUSON CUPOLA.]

_Mougin's Rolled Iron Cupola_.--The general form of this cupola (Fig. 1)
is that of a cylindrical turret. It is 123/4 feet in diameter, and rises
31/4 feet above the top of the glacis. It has an advantage over the one
just described in possessing more internal space, without having so
large a diameter; and, as the embrasures are at right angles with the
sides, the plates are less weakened. The turret consists of three plates
assembled by slit and tongue joints, and rests upon a ring of strong
iron plate strengthened by angle irons. Vertical partitions under the
cheeks of the gun carriages serve as cross braces, and are connected
with each other upon the table of the hydraulic pivot around which the
entire affair revolves. This pivot terminates in a plunger that enters a
strong steel press-cylinder embedded in the masonry of the lower
concrete vault.

The iron plate ring carries wheels and rollers, through the intermedium
of which the turret is revolved. The circular iron track over which
these move is independent of the outer armor.

The whole is maneuvered through the action of one man upon the piston of
a very small hydraulic press. The guns are mounted upon hydraulic
carriages. The brake that limits the recoil consists of two bronze pump
chambers, a and b (Fig. 10). The former of these is 4 inches in
diameter, and its piston is connected with the gun, while the other is 8
inches in diameter, and its piston is connected with two rows of 26
couples of Belleville springs, d. The two cylinders communicate through
a check valve.

When the gun is in battery, the liquid fills the chamber of the 4 inch
pump, while the piston of the 8 inch one is at the end of its stroke. A
recoil has the effect of driving in the 4 inch piston and forcing the
liquid into the other chamber, whose piston compresses the springs. At
the end of the recoil, the gunner has only to act upon the valve by
means of a hand-wheel in order to bring the gun into battery as slowly
as he desires, through the action of the springs.

[Illustration: FIG. 10.--MOUGIN'S HYDRAULIC GUN CARRIAGE.]

For high aiming, the gun and the movable part of its carriage are
capa