Reversible transit circle, Cape Town, South Africa, 1909.
© Science Museum / Science & Society Picture Library
Photograph of the reversible transit circle, an astronomical measuring instrument, at the Cape Observatory, in South Africa. Made by T Cooke & Sons Ltd, the instrument was used in conjunction with an accurate timepiece called a regulator clock. The transit circle was used to measure the position of stars as they cros the north-south meridian and to check the running and accuracy of clocks.