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The Metre – the repeating circle & triangulation

The Metre (meaning measure) was one ten-millionth of the distance from the North Pole to the Equator! France embarked on a first large scale measurement. It took 7 years to measure the distance from Dunkirk to Barsalona. They used triangulation with an instrument called the Repeating Circle along with trigonometry.

The standardization of measurement: the Metre

Creating the Metre – a universal standard

By the 16th century, there we over 250,000 weights and measures in Europe. This effected trade, navigation, building plans, etc. Fire hoses would not connect from town to town. France chose to create a standard by measuring something unchangeable. They chose the Earth. Before this standardization, the human body (the Ruler of the land) would make new measurements upon gaining power.

The Repeating Circle

Repeating Circle
Repeating Circle


This is one of two double repeating circles that Ferdinand Rudolph Hassler, the first superintendent of the U. S. Coast Survey, ordered from Edward Troughton in London in 1812, and that was shipped in 1815. The large circle may be angled from vertical to horizontal to the opposite vertical position. It is graduated to 10 minutes, and read by four verniers and two magnifiers to single minutes.

A repeating circle is a geodetic instrument with two telescopes that is designed to reduce errors by repeated observations taken on all parts of the circumference of a circle. The form was developed by the Chevalier de Borda, first executed by Etienne Lenoir in Paris around 1789, and popular for about 50 years.

Ref: F. R. Hassler, “Papers on Various Subjects Connected with the Survey of the Coast of the United States,” Transactions of the American Philosophical Society 2 (1825): 232-420, on 315-320 and pl. VII. “The Repeating Circle Without Reflection, as made by Troughton,” in The Cyclopaedia: or, Universal Dictionary of Arts, Sciences, and Literature, edited by Abraham Rees (London, 1819), Vol. VII, Art “Circle.”

Image credit:

NAME: repeating circle MAKER: Troughton and Simms PLACE MADE: United Kingdom: England, London MEASUREMENTS: overall: 32 1/8 in x 26 3/4 in x 17 in; 81.6356 cm x 67.945 cm x 43.18 cm upper circle: 17 1/2 in; 44.45 cm circle at base: 13 1/2 in; 34.29 cm telescope: 24 in; 60.96 cm overall; base: 16 3/4 in x 15 1/4 in x 16 in; 42.545 cm x 38.735 cm x 40.64 cm overall; horizontal circle: 13 in x 23 in x 20 in; 33.02 cm x 58.42 cm x 50.8 cm ID NUMBER PH.314640 CATALOG NUMBER 314640 ACCESSION NUMBER 208213

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