The photograph shows the decaying framework of William Herschel's forty-foot telescope. This experimental negative, silver on glass, is the earliest of a photograph on glass. The image has deteriorated badly and is barely visible. Sir John Herschel (1792-1871), was an English astronomer, mathematician and chemist and the son of Sir William Herschel. Herschel introduced 'hypo' (thiosulphate) as a photographic fixerative and discovered the cyanotype or blueprint process in 1842.
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