antik.it/Nautical-antiques/8093-Antique-Sextant/
1739291793Code 8093 Antique SextantBrass sextant signed H.G. Blair & Co 53, James St. Cardiff, from the second half of the 19th century and housed in its original mahogany wood box with brass handle, hinges and clasps, complete with lock and key. Silver flap and vernier, wooden handle, 3 colored glasses for the fixed mirror and 4 for the mobile one, three telescopes, 1 filter, 1 recording key, vernier graduated from 0 to 150°, index and horizon mirror. Conservation status: very good, functional and complete with custom-made support base made of wood and brass. Box measures 25.5x23x13 cm – 10x9.1x5.2 inches
Blair & Co was founded in Bristol in 1829 by John Blair, the company remained in Bristol until the owner decided to move to Cardiff to expand trade in South Wales. In 1926 a general strike paralyzed all shipping and Blair was forced to hand over the company to a consortium of local shipowners. In 1927 the company changed its name to Blairs Nautical Supplies. The typist Nellie Ramsay together with her sister Mabel joined the company in 1908, becoming the owners and retiring from the business in 1970.
The sextant is an ancient astronomical instrument used to measure the height of a star (for example the Sun): the instrument is placed in a vertical plane and, looking through the aiming device, the horizon line visible through the non-silvered half of the fixed mirror is sighted. By moving the alidade, with which the mirror is integral, the light rays coming from the star and subsequently reflected from the movable mirror and from 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, coincides 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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Nautical antiques
Code 8093 Antique Sextant
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