Theodolites have been used to measure horizontal and vertical angles by surveyors since the 1500s. They allow a surveyor to fix a position on the surface of the earth, marking latitude, longitude, and height above sea level, and then map out roads, towns, and plots of land.
Transit theodolites first appeared in the 1840s, the term transit indicates that the telescope can be rotated about the horizontal axis pivoting through 180 degrees and allowing the viewer to easily see both forwards and backwards through the instrument. By 1868 they had become a "favourite instrument" of surveyors , and in the 21st century they are still used in a modern form. The manual method of reading the theodolite has been superseded by automatic reading, and the body of the instrument has become more compact and lighter.
With rapid urban expansion, one of the most important needs of the new colony was to survey and map the landscape of both Sydney, and the Colony's interior. Theodolites, such as this one, were instrumental to the colony's surveyors, and would have played an important part in their everyday work.
This theodolite was made by Troughton and Simms, who were significant scientific instrument makers of the 19th century. The Museum has other sizes of Troughton and Simms theodolites in the collection, as well as other instruments such as telescopes.
This transit theodolite remains of national significance due to its pioneering role in Australian science and its association with Australia's earliest surveyors and astronomers. It is also significant for its association with nineteenth century surveying instruments and instrument makers.
J. A. Bennett, The Divided Circle, Christies Pty, 1987 pg 90
W. D. Haskoll, Land and Marine Surveyors, London, 1868, pg 81.
J. A. Bennet and O. Brown, The [Compleat] Surveyor, The Whipple Museum of the History of science, 1982. pg 17
Written by Erika Dicker, Assistant Curator, November 2007.