Development of Photography from The Cambridge Dictionary of Scientists
Photography uses two basic principles, both longknown: firstly, a lens to form an image, as in the ‘camera obscura’ (a box with a lens in one end that forms an image on a screen at the other end for an artist to trace or copy); secondly, the sensitivity to light of some chemical compounds, mostly silver halides. Around 1800 Thomas Wedgwood, aided by his friend Davy, tried to use these two principles to make stable images, but had little success. He used paper soaked in silver nitrate, but it was not sensitive enough to use in a camera, and his best results were shadow pictures of leaves and similar objects, obtained by placing them in contact with his paper and exposing to sunlight, when the uncovered areas blackened. He failed to find a way of ‘fixing’ the result, which blackened entirely on viewing in daylight.