Introduction by John Herschel

Sir John Friedrich Wilhelm Herschel, the first generation slave baron, FRS, KH (Sir John Frederick William Herschel, 1st Baronet, March 7, 1792-May 11, 1871) was born in Slough, Buckinghamshire, England, the son of a famous astronomer, mathematician, chemist and photographer and astronomer William Herschel. John Herschel was the first to record the date of astronomical phenomena by the method of Julian calendar, and he also made great contributions to the development of photography. He found that sodium thiosulfate can be used as a fixing agent for silver bromide. He created such terms as photography, negative film and positive film.