Summary

This speculum mirror is the only one remaining of the two that were shipped to Australia in 1868 as part of the Great Melbourne Telescope. It was cast by Thomas Grubb, at his Rathmines Road engineering workshop in either September or November of 1866, and the subsequent cooling, grinding and polishing of each mirror to its final figure was completed by early 1867.

Two mirrors were required so that while one was in use in the telescope, the other could be serviced to remove tarnish and maintain its optical figure. Both were transferred to Mount Stromlo Observatory in the late 1940s when the telescope was acquired by the Australian Government, however neither were used in a telescope again. One was accidently broken at Mount Stromlo, but this remaining one was displayed on the wall of the new observatory where the telescope was reconfigured with a 50 inch primary glass mirror. The speculum mirror was acquired by the museum in 1984, along with many other remaining parts of the original Great Melbourne Telescope that were no longer required, and placed into storage.

In 2013, the Museum was approached by Simon Starling, an English conceptual artist, who displayed the mirror as part of his newly commissioned artwork at MUMA (Monash University Museum of Art), as part of the retrospective "Simon Starling: In Speculum". He also produced photographs of reflected objects in the mirror for the exhibition.

Physical Description

A 48 inch diameter (4.5 inches thickness) bronze (55% copper, 45% tin) speculum metal (mirror supported within a light green painted metal surround. Hole in centre of mirror.

Significance

This items was originally registered under ST 038755.2 as part of the GMT telescope, but as this mirror and its mounting will not be used as part of the restored telescope, and will be replaced with a replica primary mirror cell and new primary mirror cell, it was determined that for curatorial reasons this items is now better managed as a separate object with its own exhibition, conservation and location history, etc. The speculum mirror is of enormous significance in its own right as one of the few surviving original speculum mirrors from the great reflectors of the late-18th and early 19-th centuries. It was originally the Great Speculum B, or duplicate primary mirror, made for use with the Great Melbourne Telescope.

The Great Melbourne Telescope was built by Thomas Grubb of Dublin in 1868 and erected at Melbourne Observatory in 1869. It was a reflector telescope with a speculum (metal) mirror of 48 inches diameter; at the time it was the second largest telescope in the world and the largest in the southern hemisphere.

The design and construction was overseen by a committee of eminent British astronomers, who developed the telescope to study the nebulae of the southern hemisphere skies. It was the first major telescope built by Thomas Grubb, and revolutionary in many aspects of its design. The firm went on to make many of the major telescopes around the world in the second half of the nineteenth century.

The telescope never lived up to expectations, due to difficulties with constant tarnishing of its mirrors, flexure in the mirrors, and its relative unsuitability for the new astronomical techniques of photography and spectroscopy.
The telescope was operated at Melbourne Observatory by a dedicated Great Melbourne Telescope Observer: Albert Le Seuer (1869-70), E F MacGeorge (1870-72), Joseph Turner (1873-83), Pietro Baracchi (1883-92); thereafter it was used only intermittently.

When Melbourne Observatory closed in 1944, the telescope was sold to the Commonwealth Observatory at Mount Stromlo, Canberra.

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