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Lot 13
THOMSON'S LUNAR CORRECTOR.
21 September 2015, 13:00 EDT
New YorkSold for US$2,500 inc. premium
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THOMSON'S LUNAR CORRECTOR.
English, c. 1820, signed "D. Thomson Invt" and "Bate London, N° 209." Boxwood, 37" long with brass fittings and cursor. Both sides of rule and slider marked with numerous scales, including on the Lunar side "App Alt.," "App. Dist.," "Hor. Par.," "Corr." and "Comp. Corr.," and on the Time side, "Half Sun," "Lat.," "Diff.," "Time P.M.," and "Time A.M.." Brass cursor engraved with Declination scale.
Invented by Captain David Thomson (1789-1834) and made and sold by Robert Bate in 1816, this extremely rare device was used for calculating the longitude at sea, and was described as a "Longitudinal Scale" or "Lunar Corrector" for reducing lunar distance observations in determining the longitude. It was endorsed by many, including Edward Troughton as giving apparent distances within a few arcseconds.
Invented by Captain David Thomson (1789-1834) and made and sold by Robert Bate in 1816, this extremely rare device was used for calculating the longitude at sea, and was described as a "Longitudinal Scale" or "Lunar Corrector" for reducing lunar distance observations in determining the longitude. It was endorsed by many, including Edward Troughton as giving apparent distances within a few arcseconds.





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