X-rays were discovered in 1895 by Roentgen while studying the phenomena of gas discharge. Using a cathode ray tube with a high voltage of several tens of kilovolts. he noticed that salts of barium would fluoresce when brought near the tube, although nothing visible w.as emitted by the tube. This effect persisted when the tube was wrapped with a layer of black originated cardboard. Roentgen soon established that the agency responsible for the fluorescence ts unknown nature, he gave this agency the name X-rays. He found that X-rays could man of at the point at which the stream of energetic electrons struck the glass wall of the tube. Be themselves by darkening wrapped phot aphic plates, discharging charged electroscope penetrate considerable rescence in a number of different substances. He also found that X-ray can as by causing rials of low atomic number. whereas substances high thicknesses of atomic number are relatively opaque R entgen took the first steps in identifying the natu rays by using a system of slits to show that they travel in straight lines, and that they are uncharged, because they are not deflected by electric or magnetic fields The discovery of X-rays aroused the interest of all physicists, and many joined in t vestigation of their properties. In 1899 I laga and Wind performed a single slit diffraction experiment with x-rays which showed that x rays are a wave motion phenomenon, and. from 1he ize of the diffraction pattern, their waveiength could be estimated to be 10" cm. In 1906 Barkl proved that the waves are transverse by showing that they can be polarized by scattering many materials