Sextant with eye pieces and case

Object numberV00006885

NameSextant

MediumMahogany wood, brass

DimensionsOverall: 124 x 330 x 270 mm, 1.6 kg

ClassificationsTools and equipment

Credit LineANMM Collection Purchased with USA Bicentennial Gift funds

Terms

DescriptionWooden (mahogany) keystone sextant case made by Spencer, Browning & Rust, London. Dated to 1850s. Although this sextant was made in England, the case contains two American instrument makers cards. One card depicts how the sextant was used for measuring lunar distances.HistoryThe sextant was developed in 1757. It is an instrument of double reflection by means of two mirrors, and thus although its actual arc subtends an angle of 60 degrees (1/6th of a circle - hence the name sextant), it is capable of measuring angles up to 120 degrees. The sextant was an improvement on the earlier quadrant, an instrument capable for measuring angles up to 90 degrees (1/4th of a circle hence the name quadrant). The capacity of sextants to read angles greater than 90 degrees was an advantage when using the lunar distance method to determine longitude. This was also useful for taking horizontal angles. SignificanceThis sextant case is representative of the high level of technological development achieved in the design and manufacture of navigational instruments in the 19th century.