In 1834 William Henry Fox Talbot (1800-77), a British scientist, began experimenting with the well-known tendency of silver nitrate to blacken when exposed to light, and on January 31st 1839 he read his paper “Account of the Art of Photogenic Drawing” to the Royal Society in London in which he acknowledged the earlier experiments of Sir Humphry Davy (1778-1829) and Tom Wedgwood and explained the processes he had been developing since he had succeeded with his first image in 1835. Talbot’s patent of 1841 on what he called the “Calotype” explained the process of exposing a semi-transparent paper soaked in silver nitrate to the light, then developing the invisible latent image and fixing it by means of chemical …
Clark, Robert. "Photography, its Invention and Early History". The Literary Encyclopedia. First published 27 September 2003; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=1264, accessed 26 April 2015.]