Saturday 28 June 2014

The 1874 Transit of Venus

"I do not suggest that photographic observations should displace eye observations; on the contrary, I think that both eye and photographic observations ought to be made." Warren de la Rue 1873 

By 1874 advances in the use of photography for astronomical observations meant it was now an indespensible part of the major astronomical event of that year, the Transit of Venus. Around the world, observatories and astronomers were busy making preparations and designing new equipment and training staff to capture the event on film.

In Sydney Henry Chamberlin Russell brought new photographic equipment and modified some of the existing telscopes to turn them into cameras. From 1871 preparations for the 1874 transit had occupied much of Russell's time as he worked to set up observation stations at Goulbourn, Woodford, Eden and Bathurst to photograph the event.

The most impressive instrument was the new 11.4 inch telescope purchased from the optician and instrument maker, Hugo Schroeder and this was installed in the South Dome of the Observatory. 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. Some of the Observatory's older instruments were transported along with the prefabricated observatories to the rural stations.

Another important instrument purchased was an astrographic telescope made by J. H. Dallmeyer which was developed especially for photographing the Venus transit. It was set up at 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. 

Geoff Barker, December, 2008

References
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
Russell, H., C., "Report of Astronomer for 1874 & 1875', New South Wales Government Printer, 1876

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