Handbook for Light Artillery

by A. B. Dyer

The scale of yards for shell, on the front face of the sight, is marked for each 100 yards of range, and is read from an index line on the slide.

The horizontal limb, or cross-bar, e, which is actuated by the screws e′e′, is graduated into spaces, each of which corresponds to a deviation equal to ¹/₃₄₅ of the range. (In future constructions this division will correspond to ¹/₁₀₀₀ of the range.) This variation is tabulated in the range table under the heading "Deflection for one division of the horizontal scale."

By means of a pivot, B, the sight proper is attached to the stem A, the axis of rotation being at the zero of the scale. The stem tapers so as to fit into the sight-socket fixed at the breech. A pin projecting from the stem, and fitting in a recess in the socket, insures the sight being properly placed on the gun.

The sight is first levelled and clamped by means of the clamp-screw a before sighting. Vertical and horizontal changes for elevation, drift, etc., are given by the thumb-screws d and e′e′.

THE POINTING ARC.

(Fig. 41a.)

This instrument, now under consideration for use with field-artillery, to replace wholly or in part the rear sight, is made principally of bronze, and comprises the arc a, the slide b, and the level-piece c.

The arc has two small seating plates, d d, secured to its base by countersunk screws.

The slide is connected to the arc by a dovetail-joint, and moves over it, the friction of a spring keeping the slide in any desired position. The tension of this spring is adjusted by the two screws on the side of the slide.