with the sight-bar at level, if a gun is aimed by it at the water-line
of a vessel at point-blank range, the shot would strike short of the
point aimed at by about one-quarter of the distance; or, if aimed,
under similar conditions, at the upper part of the hull, the shot
would fall a distance below the point aimed at equal to the height of
the gun.

294. In firing at small objects, particularly boats, within
point-blank range, it is therefore important to attend to this source
of error. It is desirable that all sights should be marked, from 100
yards to the greatest range, and thus avoid all consideration of
point-blank.

In fitting new guns, or those upon which the sights require replacing,
the sight-bar will be fitted as described in Article 289, and
graduated from 100 yards downwards.

For shell-guns the ranges are marked for shells on the sight-bars, in
the same manner as those for the shot of shot-guns.

295. These sights being each adjusted to a particular gun, and marked
with its class and number, do not, in strictness, admit of being
transferred to other guns, even of the same class.

296. When used, the stem of the breech-sight must be raised or
lowered, to correspond with the ascertained or estimated distance, in
yards, of the object aimed at, and firmly secured there by the
thumb-screw. Then, if the ship be steady, elevate or depress the gun
until the line of sight from the bottom of the notch of the
breech-sight, the top of the reinforce-sight, and the point to be
struck, will coincide; but if the ship have a rolling motion the gun
must be so laid, after the sight is set for the distance, that this
coincidence may be obtained, if possible, at the most favorable part
of every roll which the ship makes.

297. The inclination of the line of metal to the axis of the bore
varies in guns of the same class, as well as in those of different
classes. Aiming, therefore, by the line of metal cannot be relied on
for definite ranges; besides that, within those ranges, it is apt to
mislead by giving too much elevation to the piece. Therefore, when the
established sights are not furnished, or have become unserviceable,
wooden dispart-sights lashed on the reinforce should be immediately
substituted. A narrow groove in the upper surface of the wooden sight,
made to coincide with the plane of the line of sight marked on the
gun, will assist the Gun Captain in getting the true direction
quickly.

Half the difference