Telescope, 11.4 inch equatorial refracting telescope, brass / glass, made by Hugo Schroeder, Hamburg, Germany, 1874, used at Sydney Observatory, Sydney, New South Wales, Australia
There are two main types of telescopes. One uses a curved reflecting mirror to capture an image of the celestial bodies the other uses a refracting lens to magnify the image.
In 1874, after two years of inquiries, the New South Wales Government Astronomer H. C. Russell acquired a number of new instruments in preparation for the upcoming Transit of Venus. One of these was a new 11.4 inch telescope purchased for the observation of double stars from the optician and instrument maker, Hugo Schroeder.
Russell was impressed by a Schroeder telescope owned by Alfred Fairfax, a Sydney jeweller and amateur astronomer, and this may have been one of the reasons he ordered the new telescope from Schroeder. A 4.5-inch Schroeder telescope owned by Fairfax was used at Woodford to observe the Transit of Venus in 1874.
As well as the telescope Russell purchased some additional instruments from Schroeder. These were a solar polarising eyepiece (H10380) designed for viewing the sun, a filar micrometer mounted on a graduated circuit (H10007) and some eyepieces (H10294). A sun diagonal (H10295) used in conjunction with the Schroeder telescope was purchased separately.
The telescope was specially made to fit into Sydney Observatory's South Dome. The original dome built in 1858 was taken down and a larger dome built to fit the telescope. The telescope had a clear aperture of 11.4-inches and a focal length 12 feet 6 inches and Russell commented that while this shortened focal length was a disadvantage to definition it was an advantage to its light catching power.
The telescope was adapted for taking photographs of the Transit of Venus in December of 1874. The setup of the lenses was also modified by Russell who, once this was completed, felt that the definition of the telescope was superb especially when using the achromatic eyepieces supplied by Dr. Schroeder. For the Transit of Venus it was fitted with a camera and enlarging lens that magnified the sun's image to four inches. The wet collodion photographic plates were placed at the end of the camera and held in place by a spring. The camera end passed into a dark room tent raised inside the dome and connected to the telescope by a flexible sleeve. A shutter was used to take the picture which was developed on the spot and another inserted immediately. Three persons working in this fashion managed to take one photo per minute. The telescope was also used by Russell on the 7th of May 1879 to measure the 'Gem' star clusters in Arago.
Over the course of the next thirty years other changes were made to both the telescope and its accessories to increase the usefulness of the instrument. The filar micrometer was worked on by the E. Esdaile, a local instrument maker, who replaced the original micrometer. In 1883 the mount for the telescope was redesigned by local manufacturer The Mort's Dock Engineering Company. Another accessory that was used with the telescope was a Star Diagonal (H10295) with an adaptor for the 11.4inch telescope. This was made by T. Cooke and Sons after 1922. Lastly a drive mechanism (H10268) made by Guster Heyde of Germany was added sometime around 1914 to drive the rotation of the telescope.
Todd, David, P., Stars and Telescopes, Sampson Low, Marston, and Co., 1900
Haynes, Raymond, Haynes, Roslynn, Malin, David, McGee, Richard, Explorers of the Southern Sky, Cambridge University Press, 1996
Airy, G. B, Account of the Observation of the Transit of Venus, 1874, December 8, Made Under the Authority of the British Government and of the reduction of the Observations, Her Majesty's Stationary Office, 1881
De-Clerq, P.R., Nineteenth Century Instruments and their Makers; Rodopi, Amsterdam, 1985
Knight, E., H., (ed), 'Knights American Mechanical Dictionary', Vol III, J.B. Ford and Company, New York, 1874
Hünsch, Matthias, Hamburg Observatory - Overview: Buildings & Telescope, http://www.hs.uni-hamburg.de/EN/Oef/Stw/aequator/aequator.html
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Russell, H., C., "Report of Astronomer for 1874 & 1875', New South Wales Government Printer, 1876
Geoff Barker, August, 2007