=Line sights.=—The line sight consists of a conical point as a front sight and a V notch as a rear sight, located on the top element of the gun. They determine a line of sight parallel to the axis of the bore, useful in giving general direction to the gun. =Front and rear sights.=—The front and rear sights are for general use in direct aiming. The front sight carries cross wires. The rear sight is of the peep variety, constructed as follows: To the sight bracket is attached the shank socket upon which a spirit level is mounted for the necessary correction due to difference in level of wheels. The sight shank consists of a steel arc, the center of which is the front sight. It slides up and down in the shank socket and is operated by a scroll gear. A range strip is attached to the face of the shank and is graduated up to 6500 yards, least reading 50 yards. To the left side of the shank is an elevation spirit level, permitting approximate quadrant elevations to be given with the sight shank when the quadrant is out of order. The peep sight and its deflection scale are mounted above the shank. This peep traverses along a screw operated by a knurled head. A socket and ratchet are also provided for the attachment of the panoramic sight. [Illustration: _Rear Sight._] Nomenclature of the important parts of the Rear Sight:— Peep sight Elevation level Deflection scale Peep sight screw and head Range strip Shank Shank socket Cross level Leveling screw Scroll gear and handle Rear sight bracket Panoramic sight socket and ratchet PANORAMIC SIGHT, MODEL 1917. Description. =The panoramic sight= is a vertical telescope so fitted with an optical system of reflecting prisms and lenses that the gunner can bring into his field any point in a plane perpendicular to the axis of the telescope. The optical characteristics of the instruments are as follows: Power = 4. Field of view = 10°. =The rotating head prism= has a movement of 600 mils in a vertical plane; movement is obtained by turning elevation micrometer. The amount and direction of rotation is indicated on a scale in the head by the elevation index and micrometer. The scale is graduated in 100-mil intervals, the micrometer in mils. One complete turn of the micrometer is equivalent to one space on the sale. The head is level when the index is opposite 3 and micrometer at zero. [Illustration: PANORAMIC SIGHT MODEL OF 1917]