it by disintegrating it into microscopic dark particles of metallic silver. Of greater potential usefulness, Scheele found that ammonia dissolved the silver chloride, but not the dark particles. This discovery could have been used to stabilize or "fix" a camera image captured with silver chloride, but was not picked up by the earliest photography experimenters. Scheele also noted that red light did not have much effect on silver chloride, a phenomenon that would later be applied in photographic darkrooms as a method of seeing black-and-white prints without harming their development. Although Thomas Wedgwood felt inspired by Scheele's writings in general, he must have missed or forgotten these experiments; he found no method to fix the photogram and shadow images he managed to capture around 1800 (see below). Elizabeth Fulhame and the effect of light on silver salts (1794) Elizabeth Fulhame's book An essay on combustion described her experiments of the effects of light on silver salts. She is better known for her discovery of what is now called catalysis, but Larry J. Schaaf in his history of photography considered her work on silver chemistry to represent a major step in the development of photography. Thomas Wedgwood and Humphry Davy: Fleeting detailed photograms (1790?–1802) English photographer and inventor Thomas Wedgwood is believed to have been the first person to have thought of creating permanent pictures by capturing camera images on material coated with a light-sensitive chemical. He originally wanted to capture the images of a camera obscura, but found they were too faint to have an effect upon the silver nitrate solution that was recommended to him as a light-sensitive substance. Wedgwood did manage to copy painted glass plates and captured shadows on white leather, as well as on paper moistened with a silver nitrate solution. Attempts to preserve the results with their "distinct tints of brown or black, sensibly differing in intensity" failed. It is unclear when Wedgwood's experiments took place. He may have started before 1790; James Watt wrote a letter to Thomas Wedgwood's father Josiah Wedgwood to thank him "for your instructions as to the Silver Pictures, about which, when at home, I will make some experiments". This letter (now lost) is believed to have been written in 1790, 1791 or 1799. In 1802, an account by Humphry Davy detailing Wedgwood's experiments was published in an early journal of the Royal Institution with the title An Account of