Double Frame Sextant by the inventor "Troughton, London" circa 1810. On the vertical limb above the scale is the engraved serial number "1086" with the word "Platina" (platinum) engraved just below. The large arc is calibrated up to 150 degrees and the unique vernier magnifier (seen as a brass disc) is backed by white porcelain to aid in observing readings. Troughton invented the double or "pillar frame" sextant in 1788, so named because it consisted of 2 thin sheet frames of brass braced together with brass pillars to form a lightweight and rigid platform on which to construct a hand-held instrument for taking celestial observations. While the double frame proved to be an effective 18th C. concept -- one which gave Troughton great notoriety as a respected instrument maker -- the complexity and cost of producing such sextants gave way to more simplified designs by the mid 1800's. (Private Collection. Ex. West Sea Co.)