Xerography (which means “dry writing” in Greek) is a proces of making copies that was invented in 1938 by Chester Floyd Carlson (1906-1968). Xerography makes copies without using ink (hence its name). In this process, static electricity charges a lighted plate; a plastic powder (called toner) is applied to the areas of the page to remain white. Carlson marketed his revolutionary device to about 20 companies before he could interest any. The Haloid Company (later called the Xerox Corporation) marketed it, and photocopying eventually became common and inexpensive.
X-rays were discovered in 1895 by Wilhelm Konrad von Roentgen (1845-1923). Roentgen was a German physicist who described this new form of radiation that allowed him to photograph objects that were hidden behind opaque shields. He even photographed part of his own skeleton. X-rays were soon used as an important diagnostic tool in medicine. Roentgen called these waves “X-radiation” because so little was known about them.