The Reflecting Circle

French Reflecting Circle, Navigational toolThe advent of the reflecting circle is generally attributed to the English, who by the mid 1700's saw makers like Ramsden, Gregory, Adams, Borda and Mayer innovating and producing such instruments. Initially these instruments were used at sea to find the longitude by the lunar distance method.

Oddly, perhaps because of the adverse reaction given to Mayer's reflecting circle by Captain John Campbell in 1758, the reflecting circle never really gained popularity on the English side of the Channel.

By the end of the 18th century, with the widespread acceptance of the marine chronometer as a more reliable tool with which to find the longitude, reflecting circles were relegated to use in hydrographic surveying and chart making. It was left to the French and Germans to refine these complex instruments during the 19th century.

The ability to measure large angles and the accuracy of averaging several observations were features which found favor on the Continent, despite the circle's inherent size and awkwardness in taking sights.

Reflecting Circle, 19th century navigational instrument


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