[填空题]The camera is often thought to be a modem invention. But as early 1727, a German physicist {{U}} (36) {{/U}} that light darkens silver salt in a chemical {{U}} (37) {{/U}}. Using a camera, a big box with a small hole to let the light in, he made {{U}} (38) {{/U}} images on the salt. Silver salt is still the {{U}} (39) {{/U}} of film today. Then a French scientist made the first {{U}} (40) {{/U}} picture by using a special {{U}} (41) {{/U}} of metal sensitized with silver salt. A photography he made in 1826 still {{U}} (42) {{/U}}. The painter, Daguerre improved on the process {{U}} (43) {{/U}} placing common salt the kind we eat on the metal. This was in 1839, {{U}} (44) {{/U}}, but the problem was the printing of photographs, and it wasn’t until other scientists developed the kind of paper we now use, that good printing was possible and photograph become truly modem. In 1860, Matthew Bradey was able to take his famous pictures of the American Civil War, {{U}} (45) {{/U}}. In