Meridian circle, St Petersburg, Russia, 1876.
© Science Museum / Science & Society Picture Library
Photograph of a meridian circle by Repsold at Pulkowa Observatory, St Petersburg. A meridian circle consists of a telescope attached to a large graduated circle. It is mounted so that the telescope revolves as though in transit in a meridian plane. Using this instrument the ascent and decline of a star can be measured in a single observation.