Optical instrument

In 1887 astronomers from around the world embarked on a massive new enterprise; known as the Carte du Ciel (Mapping the Stars) project it involved photographing and measuring the stars in both hemispheres. Australia was actively involved in project with observatories in Sydney, Melbourne, and Perth keen to participate in this international project. Each observatory was allocated a zone of the sky and was expected to record it using instruments of a standard pattern.

This instrument was used in conjunction with the photographic plates taken with the astrographic cameras supplied for the 'Mapping the Stars' project. Originally the plates were to be measured at a central plate-measuring facility in Paris but when this failed to materialise Melbourne and Sydney set up a shared facility located in Melbourne. By 1915 there was a huge backlog of unmeasured photographs and Sydney Observatory purchased its own plate measuring machines to try to clear the backlog.

Although made by Troughton and Simms this machine was based on an innovative design by Professor H.H. Turner. Turner found that the screw system initially used to measure plates was very labour intensive and instead devised an eyepiece scale measuring machine. This reduced the time taken to measure the stars on each photographic plate.