Transit of Venus portable altazimuth circle, 1876.

Photograph of a universal circle, an astronomical measuring instrument, which was used to observe the 1874 Transit of Venus. It was part of the equipment supplied to the five British expeditions, sent around the world to view and measure this rare event. It gave astronomers an opportunity to accurately determine the size of the Solar System. The base upon which the instrument stands indicates that it was used at Station D (New Zealand?). After a period of over a hundred years the next transits of Venus occur in 2004 and 2012.