X-rays were first discovered by a German scientist , Wilhelm Konrad Rontgen , in 1895 , almost by accident . He and several other scientists were experimenting with passing electric currents through certain gases in a special glass tube from which the air had been moved . One day Rontgen noticed that , even when the tube was covered with black paper , some strange kind of radiation was coming through and making a screen nearby glow. Rontgen could not see anything coming out of the tube ,but then he discovered that if he put the screen in the next room on the other side of a closed door , the rays could pass not only through black paper but also through wood .