The Transit of Venus on 6 June 2012 is the latest occurrence of an event that has shaped the scientific history of Australia. Captain Cook’s expedition to observe the 1769 transit in Tahiti led to the European settlement of Australia. The 1874 transit may not have been quite as auspicious but it did lead to some major advances in the use of photography for astronomical observations.
Sydney Observatory was part of this pioneering enterprise and like other observatories around the world began designing new equipment and training staff to capture the event using cameras. The New South Wales Government Astronomer in Sydney, Henry Chamberlain Russell, had been diligently working on these preparation for around three years and photography had occupied much of his time.
New photographic equipment was brought and existing telescopes modified to turn them into cameras. These preparations were not just limited to Sydney as Russell also set up observation stations at Goulbourn, Woodford, Eden and Bathurst to photograph the event.
In 1874, after two years of inquiries, Russell acquired a number of new instruments in preparation for the upcoming Transit. 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 had been 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. Fairfax’s smaller 4.5-inch Schroeder telescope was used at Woodford to make observations of the Transit.
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.
Perhaps the most unique camera acquired was the Janssen photoheliograph (H10211). Made by J. H. Dallmeyer, it was based on a unique design by Janssen and had been approved for use at the five other observatories that were part of the British Royal Observatory Transit of Venus program. The others went to Honolulu, Mokkatam, Rodriguez, Kereguelen and Burnham.
For the Transit of Venus it was set up in Woodford in the Blue Mountains at the residence of A. Fairfax. There were seven observers present for the occasion: P. F. Adams Surveyor-General; Hirst a well known amateur astronomer; Mr. Vessy of the Trigonomical Survey; Mr. Du Faur of the Survey Department; Mr. Bischoff the photographer and two unnamed carpenters.
It took specially made 6.5 inch circular photographic plates (H10379) and Unfortunately of the 14 Janssen plates taken at Woodford none have survived. Twelve of the resulting Jansen photographs (60 on each plate), and 36 normal plates were sent to the Royal Observatory in Greenwich and have since been lost. The whereabouts of the other two is not known although they may have found their way into the New South Wales Government Printing Office.
One reason the plates which were sent to England were not well cared for is that, like the other photographs sent in from observatories around the world, the plates proved to be less than successful. The reasons for this were described by George Airy, Astronomer Royal at the Greenwich Observatory, in 1881, “After laborious measures and calculation it was thought best to abstain from publishing the results of the photographic measures as comparable with those deduced from telescopic view. The consideration which led to this decision are … that, however well the Sun’s limb on the photograph appeared to the naked eye to be defined, yet on applying to it a microscope it became indistinct and untraceable”
However while the photographs proved less than successful the observations themselves played an important part in the official report made by Captain Tupman to the British Government. Of the 61 reliable reports of Venus crossing the sun which were recorded at points around the entire British Empire 22 were from Australia.
Geoff Barker, 2012
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