www.antik.it/Nautical-antiques/7353-Antique-Sextant/
1656410910Code 7353 Antique SextantBrass sextant signed J. Coombes Optician & Instruments Maker Devenport from the second half of the 19th century, complete with optics and housed in its beautiful original mahogany wood box with retractable handle, brass hooks and hinges. Flap and vernier in engraved silver, handle in boxwood, 3 colored glasses for the fixed mirror and 4 for the mobile one, two telescopes, two filters with dark lenses, a microscope for reading the vernier, graduated from or to 150 ° and key pin for adjustments, index and horizon mirror. Inside the lid is fixed the certificate of analysis / revision on paper issued in July 1911 by the National Physics Laboratory Kew Observstory Richmond Surrey. Owner Name A. G Nack R.N. it is engraved on the vernier. Box size 27x25 cm h 13 – inches 10.6 x 9.75 x 5.2 . Conservation status: very good, fully functional, complete with custom-made support base.
Company founded in 1805, they were manufacturers of scientific and optical instruments at The Observatory ", Fore Street in Devonport (founded in 1806) and produced sextants for the Royal Navy and Britannia Royal Naval College.
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 °, that is to say one sixth of a circumference, hence the name, at the top of which a mobile alidade is pivoted on which a mirror that rotates with it is fixed. On the back of the mirror there is a support with a telescope oriented towards a second mirror, silver only for one half, which allows you to simultaneously observe the marine horizon, in alignment, and the pointed star, whose image is reflected by the fixed mirror to the alidade and then to the silver part of the mirror. By adjusting the position of the index of the alidade it is possible to make the image of the horizon collimate with that of the star and obtain the angle between the horizon and the star on the graduated scale of the 60 ° sector. To measure the height of a celestial body (for example the Sun) with a sextant, place the instrument in a vertical plane and, looking through the aiming device, sight the horizon line 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 star and subsequently reflected by the moving 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, coinciding with the horizon line. The height of the star is expressed by the angle whose value is read on the graduated scale. The filter is used when the star to be sighted is the Sun.
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Nautical antiques
Code 7353 Antique Sextant
Antik Arte & Scienza sas di Daniela Giorgi - via S. Giovanni sul Muro 10 20121 Milan (MI) Italy - +39 0286461448 - info@antik.it - www.antik.it - Monday-Saturday: 10am-7pm
