alls in the vicinity of
the embrasure are protected by thick iron plate. The rectangular armor
plate of rolled iron rests against an elastic cushion of sand compactly
rammed into an iron plate caisson. The conical embrasure traverses this
cushion by means of a cast-steel piece firmly bolted to the caisson, and
applied to the armor through the intermedium of a leaden ring.
Externally, the cheeks of the embrasure and the merlons consist of
blocks of concrete held in caissons of strong iron plate. The
surrounding earthwork is of sand. For closing the embrasure, Commandant
Mougin provides the armor with a disk, c, of heavy rolled iron, which
contains two symmetrical apertures. This disk is movable around a
horizontal axis, and its lower part and its trunnions are protected by
the sloping mass of concrete that covers the head of the casemate. A
windlass and chain give the disk the motion that brings one of its
apertures opposite the embrasure or that closes the latter. When this
portion of the disk has suffered too much from the enemy's fire, a
simple maneuver gives it a half revolution, and the second aperture is
then made use of.

_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 191/2 feet, and the dome is 8 inches in thickness and has a radius of
161/2 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.