Octant, late 18th century.
© Science Museum / Science & Society Picture Library
Navigational reflecting instrument in bras with ebony divided on ivory, made by Watkins of Charing Cros, London. An octant is used in surveying and in navigation to measure the angle between two objects. Octants were used by navigators to determine a ship's latitude by measuring the angle between the horizon and a celestial body, such as the Sun.