A portrait of John Herschel by the British photographer Julia Margaret Cameron (1815 - 1879), taken in April 1867. Albumen silver print. John Herschel (1792-1871) was the son of astronomer Sir William Herschel, and he extended many of his father's astronomical observations. He established the Slough reflecting telescope near Capetown, South Africa, won the Copley Medal of the Royal Society for his Cape Observations (1847), and made important contributions to other branches of science. As photographer, he invented the process of fixing film using hyposulphite of soda and coined the terms positive and negative.