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Photoheliograph telescope, made by J H Dallmeyer, 1873 - 1874
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Object statement
Telescope, photoheliograph, metal / glass, designed by Janssen and De La Rue, made by J H Dallmeyer, London, England, 1873-1874, used at Sydney Observatory, Sydney, New South Wales, Australia
"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

This is one of the most significant telescopes held in the Powerhouse museums collection. While not officially part of the British Government's observation program this telescope was purchased by Sydney Observatory and sent to Australia in 1874 along with attachments to photograph the Transit of Venus. A special stand was constructed in Sydney to support it during the observations. The telescope was made by J.H. Dallmeyer and was among the first to be used for astronomical photography in Australia.

For the observation of the Transit of Venus this telescope 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.

The telescope and attachments are the same as those at five other observatories who were part of the Royal Observatory Transit of Venus program. The others went to Honolulu, Mokkatam, Rodriguez, Kereguelen and Burnham. It was made by J. H. Dallmeyer to accommodate a special piece of photographic apparatus designed by Janssen and de la Rue which took 6.5 inch circular photographic plates (H10213 & H10379).

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. Only one of the unexposed Janssen plates has survived (H10379). 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"

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 British Empire 22 were form Australia.

Geoff Barker, August, 2007

References
Todd, David, P., Stars and Telescopes, Sampson Low, Marston, and Co., 1900
De-Clerq, P.R., Nineteenth Century Instruments and their Makers; Rodopi, Amsterdam, 1985
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
Russell, H., C., "Report of Astronomer for 1874 & 1875', New South Wales Government Printer, 1876
Russell, H., C., 'Scientific Papers 1871 to 1879', New South Wales Government Printer, 1879
Russell, H., C., Observations of the Transit of Venus, 9 December, 1874; made at Stations in New South Wales, Charles Potter, Government Printer, 1892
Knight, E., H., (ed), 'Knights American Mechanical Dictionary', Vol III, J.B. Ford and Company, New York, 1874
The photoheliograph was made between 1873 and 1874 by J H Dallmyer in London, England.
The photoheliograph was owned by the Sydney Observatory, Stock No. 293 and used to observe the Transit of Venus in 1874 from Woodford, NSW (information taken from the blue file).

 This text content licensed under CC BY-NC.

Description
Telescope, photoheliograph, metal / glass, designed by Janssen and De La Rue, made by J H Dallmeyer, London, England, 1873-1874, used at Sydney Observatory, Sydney, New South Wales, Australia

An astrographic photoheliograph telescope that can be divided into three parts, each part consisting of a brass tube with a glass lens. A brass rod with a screw guage on one end attaches to the photoheliogrpah. Various components including a brass bracket and various sized screws accompany the telescope.
Observatory stock number 293

Made: Dallmeyer, J H; London, England; 1873 - 1874


Used: Sydney Observatory; Woodford, New South Wales; 1874
H10211
Production date
1873 - 1874
Diameter
250 mm

 This text content licensed under CC BY-SA.
This object belongs to:
Sydney Observatory Collection
Subjects
+ Transit of Venus
+ Astronomical equipment
+ Scientific equipment
+ Sydney Observatory
+ Australian culture
+ Astronomy
+ Photography
+ Russell, Henry Chamberlain
+ Astronomical telescopes
Currently on public display
+ By the Light of the Southern Stars Exhibition, Sydney Observatory
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Concise link back to this object: http://from.ph/231198
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{{cite web |url=http://from.ph/231198 |title=Photoheliograph telescope, made by J H Dallmeyer |author=Powerhouse Museum |accessdate=24 November 2014 |publisher=Powerhouse Museum, Australia}}


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