1693669870Code 7655 Small SextantSmall sextant in brass, signed S.te des Etablissements Gaumont Paris 146, datable around the end of the 19th century. Instrument complete with optics and housed in a beautiful original walnut square box with original key, hinges, handle and closing hooks in brass. Brass frame with engraved silver protractor scale recessed in the arch, with scale from 0 to +130, silver flap and vernier, wooden handle, 1 colored glass for the fixed mirror and 2 for the mobile one, a telescope and a key adjustment, index and horizon mirror. State of conservation: very good, complete with support base made of wood and custom-made brass. Box measures 22 x 19 h 11.5 cm – 8.7 x 7.5 x 4.6 inches. Léon Gaumont France (1864 -1946), engineer was an inventor, entrepreneur and founder in 1895 of a historic film production company, still today recognized as one of the most important in France.
The sextant is an optical instrument used in astronomical navigation to measure the height of the stars above the horizon, in order to obtain the geographic coordinates relative to the ship's point. It has the shape of a circular sector of 60°, i.e. one sixth of a circumference, hence the name, at whose vertex a mobile alidade is pivoted on which a mirror is fixed which rotates with it. On the back of the mirror there is a support with a telescope oriented towards a second mirror, only half silvered, which allows you to observe the marine horizon at the same time, in alignment, and the pointed star, whose image is reflected by the fixed mirror to the alidade and subsequently from the silver side of the mirror. By adjusting the position of the alidade index it is possible to make the image of the horizon collimate with that of the celestial body and obtain the angle between the horizon and the celestial body on the graduated scale of the 60° sector. To measure the height of a star (for example the Sun) with a sextant, place the instrument in a vertical plane and, looking through the sighting device, sight the line of the horizon visible through the non-silvered half of the fixed mirror. By moving the alidade, with which the mirror is integral, the light rays coming from the celestial body and subsequently reflected by the movable mirror and by the silver half of the fixed mirror are sent back by the latter in the direction of observation: if one looks through the aiming device, one sees the image of the star, obtained by double reflection, coincide with the line of the horizon. The height of the star is expressed by the angle whose value is read on the graduated scale. The filter is used when the target star is the Sun.
It was Sir Isaac Newton who invented the principle of double reflection in navigation instruments, but this research was never published. Subsequently, two men independently discovered the sextant around 1730: John Hadley (1682-1744), English mathematician, and Thomas Godfrey, (1704-1749), American inventor. But it was only in 1758 that Admiral John Campbell carried out a series of tests in the open sea to experiment with a new method which relied on the lunar distance as a means of calculating longitude. This is how the sextant was developed. Initially produced in brass, they had scales divided with great precision by mathematicians who made scientific instruments.
