Notebook belonging to Sir John Herschel's, English astronomer, 1839.
© Science Museum / Science & Society Picture Library
Pages from an experimental notebook of Sir John Herschel (1792-1871) dated 11-13 February. The page shows photogenic drawing negatives with notes on 'fixing' photographs. Son of Sir William Herschel, Sir John Herschel introduced 'hypo' (thiosulphate) as a photographic fixerative and discovered the cyanotype or blueprint proces in 1842.