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Description: | LO 114 (departmental catalogue number in aluminium paint). D. Adams, Charing Crofs, London. 0-125 (scale divisions of 20 min engraved on ivory). o-20 ( vernier scale divisions engraved in ivory). MANU Dudley Adams circa 1800 22, Fleet Street (near Charing Cross), London, England. DES after CAMPBELL,John,Captain. 1757 London, England DES after BIRD,John. 1757 London, England. DES after DAVIS,John. 1594 London, England. Astronomical sextants had been in use from the sixteenth century, however, this type of marine sextant became a useful instrument after the introduction of the lunar distance method in 1757. This required greater accuracy than the quadrant could achieve. The name sextant refers to a sixth of a circumference, that is sixty degrees. As in Hadley's quadrant the mirror halves the scale so that the sextant can measure angles to one-hundred and twenty degrees. In modern usage all such instruments regardless of size of scale are called sextants.
This 16 inch instrument, with a combination of six shades two green and four red, has a 350mm radius scale and can be read to 1 sec. The index arm is reinforced with a tangent screw clamp. The frame has three arched struts and is fitted with a telescopic backsight. | License: | http://www.hmag.gla.ac.uk/spirit/rights/ | Publisher: | Hunterian Museum and Art Gallery, University of Glasgow | Rights holder: | Hunterian Museum and Art Gallery, University of Glasgow | Subjects: | SCIENTIFIC COLLECTION : | Source: | Hunterian Museum | Creator: | Hunterian Museum and Art Gallery, University of Glasgow | Identifier: | http://www.huntsearch.gla.ac.uk/cgi-bin/... | Language: | en-GB | Go to resource |
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