ble of revolving around a strong pin, c, so placed that the axis of
the piece always passes very near the center of the embrasure, thus
permitting of giving the latter minimum dimensions. The chamber of the 8
inch pump is provided with projections that slide between circular
guides, and carries the strap of a small hydraulic piston, p, that
suffices to move the entire affair in a vertical plane, the gun and
movable carriage being balanced by a counterpoise, q.

The projectiles are hoisted to the breech of the gun by a crane.

Between the outer armor and turret sufficient space is left for a man to
enter, in order to make repairs when necessary.

Each of the rolled iron plates of which the turret consists weighs 19
tons. The cupolas that we have examined in this article have been
constructed on the hypothesis than an enemy will not be able to bring
into the field guns of much greater caliber than 6 inches.--_Le Genie
Civil_.

* * * * *

HIGH SPEED ON THE OCEAN.

_To the Editor of the Scientific American_:

Although not a naval engineer, I wish to reply to some arguments
advanced by Capt. Giles, and published in the SCIENTIFIC AMERICAN of
Jan. 2, 1886, in regard to high speed on the ocean.

Capt. Giles argues that because quadrupeds and birds do not in
propelling themselves exert their force in a direct line with the plane
of their motion, but at an angle to it, the same principle would, if
applied to a steamship, increase its speed. But let us look at the
subject from another standpoint. The quadruped has to support the weight
of his body, and propel himself forward, with the same force. If the
force be applied perpendicularly, the body is elevated, but not moved
forward. If the force is applied horizontally, the body moves forward,
but soon falls to the ground, because it is not supported. But when the
force is applied at the proper angle, the body is moved forward and at
the same time supported. Directly contrary to Capt. Giles' theory, the
greater the speed of the quadruped, the nearer in a direct line with his
motion does he apply the propulsive force, and _vice versa_. This may
easily be seen by any one watching the motions of the horse, hound,
deer, rabbit, etc., when in rapid motion. The water birds and animals,
whose weight is supported by the water, do not exert the propulsive
force in a downward direction, but in a direct line with the plane of
their motion. The m