The theory of photography was born from the discovery of the phenomenon of the camera obscura: light entering a dark room through a small hole projects an identical inverted image onto the interior wall of the exterior stage. The first records of scientists recognizing this concept are found in the writings of the Greek philosopher Aristotle (384 – 322 BC). Early models of the Camera Obscura were large chambers that the artist could enter. At first, this invention was recognized as an aid to artists who could trace images to create a more realistic impression of the scene. The problem with the room was that it was not easily transportable and was therefore useless for an artist. This problem was solved thanks to advances made in the 17th century, when inventors developed a portable version of the optical device. Furthermore, those who used the instrument found that the image produced was inaccurate to the extent that it defied the rules of perspective because it was formed by a single lens. The inventors discovered a way to correct this problem, as the History of Photography explains: "By combining two lenses ground on arc segments of different radii, a reasonable flatness of the field could be obtained. And by using lenses of different focal lengths, the angle of view could be narrower for portraits and wider for landscape work” (Newhall 9). As the use of this tool became widely practiced among artists, experimenters began to realize the possibilities of the lens. invention. The idea that images formed by the Camera Obscura could be recorded as permanent prints arose in the 1790s, when Thomas Wedgwood began experimenting with photosensitive silver salts. The discovery of the effect of light on certain chemicals was made middle of paper...... five prints by Brady and his team amount to over seven thousand. Unlike Fenton's romantic style, Brady's photos told a much more graphic story, influencing Americans around the world. Other prominent photographers whose prints moved audiences were Jacob August Riis (1849 – 1914) and Lewis W. Hine (1874 – 1940). At twenty-one, Danish photographer Riis immigrated to the United States, where he discovered the poor side of New York. Four years after his arrival, Riis was given the job of police reporter. He aspired to social reform and published a book describing the state of the slums, illustrated with drawings based on his original photographs. Lewis Hine photographed factories and children working in coal mines in an attempt to raise awareness among the upper class, leading to the fall of child labor in America.