TitleBorda circle with oak box Date1900sAbout this objectKnown as a Borda circle, this navigational instrument is a type of reflecting circle used primarily in celestial navigation. It allows mariners to measure the angular distance between a celestial object and the horizon, aiding in the calculation of longitude at sea.
The Borda circle represents a refinement of earlier reflecting instruments. In the 1770s, French mathematician and Navy officer Jean-Charles de Borda, working with instrument maker Étienne Lenoir, repositioned the telescope and mirrors to simplify alignment and improve accuracy. Their 1777 design became the definitive form, eliminating the need to manually verify mirror parallelism, which was a common source of error in earlier models. Object No.88.57Inscriptions & marksLenoir à Paris N° 235' engraved on thin arm adjacent to the telescopeDimensionsH: 318mm
W: 288mm
D: 185 mmMaterialBrassGlassSourceLa Perouse MuseumCredit lineGift of Matra (Mécanique Aviation Traction)Acquisition date32266On displayNoTypeMuseum objectsOrganisations (Detailed entries)La Perouse Museum (La Perouse, N.S.W.)ThemesEuropean arrivalsScience and communication
