Sextant
an instrument for measuring the angular distance of objects by means of reflection. The principle of its SEXTON construction depends on the theorem that if a ray of light suffer double reflection the angle between the original ray and its direction after the second reflection surfaces. The instrument of which this theorem is the principle is a brass sector of a circle in outline, the sector being the sixth part of a complete circle, for which reason the instrument is called a sextant. It consists of a graduated limb, forming about the sixth part of a circle.
Two mirrors, the index mirror (1) and the lower part of the horizon glass at 5, have for object the reflection of the rays of light coming from the object under observation. The telescope (2) collects and transmits to the eye the rays of light emanating from the horizon glasses. An index and a vernier (13) permit mit the reading, on the graduated limb, of the quantity of light which the mirror has turned. When observing altitudes, the instrument is held eld perpendicularly to the horizon in the plane of the line joining the two objects. In taking noon observations at sea, to determine the latitude, the observer takes his place shortly before meridian, and turning down one or several of the shades, to prevent his eye eral of the shades, to prevent his eye telescope or site tube to the sun, moving the index so as to bring its reflected image to coincide with the sea horizon; as the sun rises, he gradually advances the limb, clamping it and using the regulating screw for this purpose, as the sun's path becomes more nearly horizontal, and slightly rocking the instrument from side to insure that it is in a vertical plane at the moment when the sun attains its greatest height. The reading of the limb at the moment when the sun begins to dip is noted, and a very simple the limb at the moment when the sun rived from the "Nautical Almanac" to the true zenith distance obtained by observation, gives the latitude. rived from the "Nautical Almanac" to church, whose duty is to take care of the sels, vestments, etc., belonging to the vessels, church, to attend on the officiating minchurch, whose duty is to take care of the ing to the church, to which is, in England, added the duty of digging and filling up graves in the churchyard.