_The Schumann-Gruson Chilled Iron Cupola_.--This cupola (Fig. 9) is
dome-shaped, and thus offers but little surface to direct fire; but it
can be struck by a vertical shot, and it may be inquired whether its top
can withstand the shock of projectiles from a 10 inch rifled mortar. It
is designed for two 6 inch guns placed parallel. Its internal diameter
is 19½ feet, and the dome is 8 inches in thickness and has a radius of
16½ feet. It rests upon a pivot, p, around which it revolves through the
intermedium of rollers placed in a circle, r. The dome is of relatively
small bulk--a bad feature as regards resistance to shock. To obviate
this difficulty, the inventor partitions it internally in such a way as
to leave only sufficient space to maneuver the guns. The partitions
consist of iron plate boxes filled with concrete. The form of the dome
has one inconvenience, viz., the embrasure in it is necessarily very
oblique, and offers quite an elongated ellipse to blows, and the edges
of the bevel upon a portion of the circumference are not strong enough.
In order to close the embrasure as tightly as possible, the gun is
surrounded with a ring provided with trunnions that enter the sides of
the embrasure. The motion of the piece necessary to aim it vertically is
effected around this axis of rotation. 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 12¾ feet in diameter, and rises
3¼ feet above the top of the glacis. It has an advantage over the one