antik.it/Nautical-antiques/7868-Antique-Sextant/
Code 7868
EUR 1600.00
In stock
1718968615Code 7868 Antique SextantBrass sextant signed Heath & C. Crayford London from the second half of the 19th century, housed in its original mahogany box, with brass clasps, handle and hinges. Silver flap and vernier, wooden handle, 3 colored glasses for the fixed mirror and 4 for the mobile one, a telescope, a filter, a microscope for reading the vernier, graduated from or to 150°, index and mirror horizon. Perfectly functional. Conservation status: very good. Complete with support base made to measure in wood and brass. Box measures 27.8x 25x12.5 cm – 10.9x9.6x4.9 inches.
The Heath & C scientific instrument manufacturing company was founded in 1845 by George Heath; his son George began his apprenticeship in the company in 1863 and became the owner in 1872. In 1882, to meet the significant increase in demand for instruments, two separate factories were built in Crayford and New Eltham. In 1937 the company was incorporated by Stanley.
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 geographical coordinates relating to the ship's point. 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 horizon line visible through the non-silvered half of the fixed mirror. By moving the alidade, with which the mirror is integral, it is ensured that the light rays coming from the celestial body and subsequently reflected by the mobile mirror and by the silver half of the fixed mirror are sent back by the latter in the direction of observation: if you look through the aiming device, you see 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 targeted is the Sun.
It was Sir Isaac Newton who invented the principle of double reflection in navigational instruments, but this research was never published. Subsequently, two men, independently of each other, discovered the sextant around 1730: John Hadley (1682-1744), English mathematician, and Thomas Godfrey, (1704-1749), American inventor. But only in 1758 did Admiral John Campbell carry out a series of tests at sea to test a new method that relied on lunar distance as a means of calculating longitude. This is how the sextant was developed. Initially made of brass, they had scales divided with great precision by mathematicians who made scientific instruments.
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Other countries: delivering on the average in 5 weekdays; custom duties charged to the buyer.
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Nautical antiques
Code 7868 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
