Photoglyphic engraving from a daguerreotype by John Mayall. Sir John Herschel (1792-1871) was an English astronomer, mathematician and chemist who discovered 525 nebulae and clusters. He pioneered celestial photography, discovering the cyanotype or blueprint proces in 1842. J J Mayall (1810-1901) made his studio one of the most commercially succesful in London, producing many albumen prints, which he showed at the Great Exhibition (1851). His company specialised in producing carte-de-vistes.
© National Museum of Science & Media / Science & Society Picture Library