Sir John Herschel (1792-1871), English astronomer. Son of Sir Frederick William Herschel, John extended many of his father's astronomical observations, including those of double stars and nebulae. He established the Slough reflecting telescope near Capetown, South Africa, and from 1834-1838 made an extensive survey of the southern skies. His Cape Observations, published in 1847, earned him the Copley Medal of the Royal Society. He also made significant contributions to photography, inventing the process of fixing film using hyposulphite of soda, and coining the terms positive and negative. From a steel engraving by Cavalier Gabrielli.