SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Detail of the photo-heliograph built for the Wilna (Vilnius) Observatory in Russia that was manufactured in 1864 by the London optical instrument maker Thomas Dallmeyer to a design by the English astronomer Warren de la Rue. After Sir John Herschel had advocated in 1857 the importance of making a daily photographic record of sunspots, the Royal Society granted support to de la Rue to design and produce a suitable instrument. The first was successfully operated at Kew from 1861. Five additional photo heliographs were made by Dallmeyer for use in observing the transit of Venus in 1874. Here, the motorised equatorial mount is shown with a section of the telescopic tube fitted with an objective of four-feet focal length that was followed by an ocular lens for projecting a magnified primary image onto the sensitised wet collodion plate.
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