Repeating circle
![12-inch repeating circle.](/Images/godic/202502/07/12in_Repeating_circle5133.jpg")
![Repeating circle on display at the Musée national de la Marine.](/Images/godic/202502/07/Cercle-reflexion-Lenoir5133.jpg")
![Mode of operation:(1) The instrument is aligned so its plane includes the two points to be measured, and each telescope is aimed at a point;(2) Keeping the angle between the telescopes locked, the left (black) telescope is rotated clockwise to aim at the right point;(3) the right (gray) telescope's position is noted, and it is rotated back to the left point.](/Images/godic/202502/07/Borda-repeating-circle.svg5133.png")
The repeating circle is an instrument for geodetic surveying, invented by Etienne Lenoir in 1784, while an assistant of Jean-Charles de Borda, who later improved the instrument. It was notable as being the equal of the great theodolite created by the renowned instrument maker, Jesse Ramsden. It was used to measure the meridian arc from Dunkirk to Barcelona by Jean Baptiste Delambre and Pierre Méchain.