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Herschel's Telescope

Herschel's Telescope

Sir John Herschel's photographic experiments consist almost exclusively of contact copies of engravings or other pictorial test objects. The only exceptions are two images of lace and an oak leaf, contact copied; and a group of camera-type images of his father's famous telescope. There are four of these in the Oxford collection, and a larger number, including several on glass, in the collection of the Science Museum, London/Bradford. That Herschel took little interest in camera images is consistent with his highly scientific approach, for although it is of obvious relevance to try such images, they do not lend themselves to a systematic series of chemical trials, since there is no effective original or control to compare the results to, while too many other variables (optical, atmospheric, meteorological, etc.) are involved.

Nevertheless one of Herschel's first experiments, on the second day (January 30, 1839) of his photographic researches, was to make an image using a Dollond telescope lens of his father's telescope. His notebook records as if with surprise that the 'image was formed in White [underlined] on a Sepia-col[oure]d ground' (the tonal reversal or negative effect seemed peculiar at first). It was a silver-based image, actually silver carbonate, and he fixed it with hypo. The exposure time was about two hours. Although mostly undated, the circular images in the Oxford and Science Museum collections seem to have been made later, during the autumn of 1839. One of those at Oxford (21527) is dated November 30, 1839. The best of them (85037) produces the same white on sepia image as his first attempt in January, and uses similar chemistry, though silver nitrate was perhaps more normal by then.

They are still essentially chemical experiments, and in particular test the chemistry under different optical conditions from his standard contact copying procedure. All four photogenic drawings of the telescope clearly use different chemical ingredients, though only two are annotated. The dark mauve sample (32127) has the appearance associated with Talbot's early salt-fixed images. Another (21527) is inscribed 'Lead paper fresh washed with NS. & used wet', indicating a paper initially treated with lead acetate, and sensitised with silver nitrate immediately before exposure. The other (11879) is inscribed 'No 608 with Hydro[?te] Pot'; Herschel by this time numbered most of his sensitising mixtures, which would be silver based, to which he has here added potassium iodide. The result (in all three) is distinctly inferior to 85037.

Their most unusual characteristic of course is their shape. Unlike Talbot, who cut his photographs into all manner of peculiar shapes, Herschel worked with regular rectangular papers of fairly consistent size (mostly sixteenths of a sheet, approximately 4 by 5 inches). The circular telescope images are cut with scissors to a diameter of about 3¾ inches (about 98mm). They have been cut prior to exposure, so it has something to do with the container they have been exposed within. The most likely reason is that Herschel contrived a makeshift camera obscura made of part of a telescope tube, perhaps utilising the Dollond lens used on January 30, the standard diameter of a portable Dollond telescope being about 3¾ inches.

November 30, 1839 falls at the very end of the first phase of Herschel's experiments, which did not resume until the autumn of 1840. In the meantime the Herschel family moved from Slough to Hawkhurst. The telescope was demolished during December 1839, so the other motivation for these photographs was to record the famous structure before it disappeared. The huge telescope tube was in a lowered position (on or near the ground), but can be seen in the best image, as can the two huts. They are thus not only the earliest photographs of a scientific instrument but the earliest 'record' photographs, deliberately taken to record a building prior to demolition. Since the photogenic drawing process was incapable of recording much detail (and in this case little more than a silhouette), Herschel also made camera lucida drawings (by hand) before the structure was demolished.

Sir William Herschel's 40-foot telescope was completed in 1789, in the garden of his home, Observatory House, Slough (near London). It was already such a well-known icon of astronomy that the Royal Astronomical Society (founded in 1820) adopted it as its symbol. Sir John Herschel, in spite of his great interest in chemistry, which he indulged for a while in his photographic researches, devoted much of his life to astronomy out of a sense of duty to continue his father's work. In this context his photographs of the telescope on the eve of its demolition, the only camera images he ever made, are poignant as well as historic.

The glass versions of the image in the Science Museum collection are the first successful photographs ever taken on glass. In 1890 (in what was then the South Kensington Museum) they were conserved, and positives made from the best one, the photographic work being done by Sir John Herschel's eldest son Sir William J. Herschel, himself a photographic experimenter and a pioneer of colour photography. Reproductions of this image with accompanying text were widely distributed, examples including the uncut sheet (63438), a bound presentation copy given by Sir W. J. Herschel to H. H. Turner in 1907 (13193), and a lantern slide version for use in lectures (13194).

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