34. What is a breech-sight?
An instrument having a graduated scale of tangents, by means of which any elevation may be given to a piece.
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35. How are the divisions of the tangent scale found?
By taking the length of the piece, from the rear of the base-ring to the swell of the muzzle, measured on a line parallel to the axis, and multiplying it by the natural tangent of as many degrees as may be required; and then deduct the dispart. Thus, for 5° elevation, and the gun supposed to be 5 feet, or 60 inches long, multiply .08748, which is the natural tangent of 5°, by 60; the product gives 5.2488 inches; supposing the dispart to be 1 inch, the graduating of the tangent scale will be 4.2488 inches.
36. With what pieces are breech-sights used?
Guns and howitzers.
37. What is a pendulum hausse?
It is a tangent scale, the graduations of which are the tangents of each quarter of a degree of elevation, to a radius equal to the distance between the muzzle-sight of the piece, and the axis of vibration of the hausse, which is one inch in rear of the base-ring. At the lower end of the scale is a brass bulb filled with lead. The slider which marks the divisions on the scale is of thin brass, and is clamped at any desired division on the scale by means of a screw. The scale passes through a slit in a piece of steel, with which it is connected by a screw, forming a pivot on which the scale can vibrate laterally. This piece of steel terminates in pivots, by means of which the pendulum is supported on the seat attached to the gun, and is at liberty to vibrate in the direction of the axis of the piece. The seat is of metal, and is fastened to the base of the breech by screws, so that the centres of the steel pivots of vibration shall be at a distance from the axis of the piece equal to the radius of the base-ring.
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