Astronomical equipment, mural circle, brass, designed and made by Edward Troughton, London, England, 1807-1809, used at Parramatta Observatory, 1815-1825
There are two main types of telescopes. One uses a curved reflecting mirror to capture an image of celestial bodies the other uses a refracting lens to gather the light. This mural circle was used in conjunction with a telescope and was set into a wall. It was then turned on an axle so the telescope could observe the stars as they passed through their meridian.
These are the remaining parts of the mural circle which arrived in Australia with Governor Brisbane in late 1821. They and presumably the telescope were made by Edward Troughton, one of the most respected instrument makers of the day. It was used at Australias first permanent observatory situated at Parramatta. After the departure of Brisbane in 1825 and the dismissal of Charles Rumker in 1830 James Dunlop was appointed Government astronomer in 1831. Upon his return to Australia Dunlop found the equipment in a bad state of repair but nevertheless he commenced observations around the middle of January 1832 using the Troughton transit (H9891) and this mural instrument.
In 1835 a new transit telescope made by Jones was delivered to the observatory which replaced the Troughton transit. The Jones telescope however proved too difficult for Dunlop to manage on his own and instead he used the Troughton mural circle (H9893) for most of his observations.
One of the consequences of this was that Dunlop's observations for the 1835 'Catalogue of 7385 Stars', the first published catalogue of stars based on observations in Australia, proved full of inaccuracies. This mistake had serious ramifications for astronomy in Australia as local Governments and British scientists maintained a degree of skepticism about the value of investing in a new observatory. The instrument was put in storage after the Parramatta observatory was closed down in 1847 and remained so until the new Sydney Observatory was built above the Rocks.
The opening of the new observatory in 1858 saw many of the original Brisbane instruments taken out of storage. Given their age it is not surprising that the new Government Astronomer Rev. W.Scott felt this instrument was substandard. Perhaps as a result the instrument was little used by Scott but his successor H.C. Russell found little wrong with the instrument and in 1872 he used it to re-observe the southern star cluster Kappa Crucis.
This mural was also significant as it may have the prototype for one of Edward Troughton's early successes. Around 1807 he submitted an innovative design for a mural circle to Nevil Maskelyne the Astronomer Royal at Greenwich Observatory around 1807. In support of his design Troughton showed the board of visitors a two foot prototype of this circle which he had made for Sir Thomas MakDougall Brisbane. This is possibly the one which is now in the Powerhouse museum's collection. Its importance can be measured by the fact that the design was accepted by Greenwich Observatory and Troughton's mural circle set for the design standard for these instruments.
Unfortunately the telescope associated with this mural circle went missing sometime after being loaned to Sydney University in 1905. But even with its faults this instrument remains of national significance due to its pioneering role in Australian science and its association with Australia's earliest astronomers. It is also significant for its association withe early nineteenth century astronomical instruments and their makers.