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Herschel, Sir John (Frederick William)

light southern photography process

[her shl] (1792–1871) British astronomer and physicist: surveyor of the southern sky.

Although his father the ‘gauger of the heavens’, did notable scientific work, John did more and ranged outside his father’s astronomical interests. For an only child his famous father was rather overwhelming, but his close friendship with his aunt ended only with her death at 98.

He graduated from Cambridge in mathematics in 1813 with the highest distinction, then began to study law, but physics attracted him. His home experiments with polarized light gave some valuable results; he also deduced that polarized light should be rotated by an electric field, as was later confirmed experimentally by . For a time, following two failed love affairs, he was uncertain of what career to follow. From 1816 he assisted his father in the study of double stars and nebulae, and thereafter he fixed on a scientific career, which was surprisingly wide-ranging. Astronomy continued to attract him and in the 1830s he decided to extend their survey of the sky to the southern hemisphere. He arrived at the Cape in 1834, accompanied by his young wife, two large telescopes, a mechanic and a children’s nurse, and in 4 years of energetic work he mapped most of the southern sky.

He worked in meteorology and geophysics and planned geomagnetic survey of the Antarctic. He was an expert chemist, and major contributions to early work on photography are due to him: he devised the cyanotype process. This used paper impregnated with an iron compound (ammonium ferricitrate), which on exposure to light formed Prussian blue. The process was simple and cheap and gave a permanent print, but the response to light was too slow for camera exposures and prints were made by placing the subject in contact with the sensitized paper and exposing to strong light (the process became much used in the 20th-c to make the ‘blueprint’ copies of engineer’s drawings and was also used at Mafeking during the Boer War, when Baden-Powell directed that bank-notes and postage stamps be reproduced during the siege).

For conventional silver-based photography he introduced ‘hypo’ as a fixing agent and was a pioneer in astronomical photography. In 1839 he made the first photograph on a glass plate (previously sensitized paper had been used), prepared the first coloured photographs of the Sun’s spectrum and introduced the words ‘negative’ and ‘positive’ into ‘photography’ (also his word), and the word ‘snapshot’. In 1850 he became Master of the Mint, a move which he was persuaded to make only by forceful appeals to his patriotism; he did the job well but without enjoyment for 5 years. At his death he was ‘mourned by the whole nation, as a great scientist and one of the last of the universalists’.

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