阅读理解

　　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．Ronghen 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．

　　The next thing he found out was that if he put his hand between the rays and a photographic plate, the rays would print a shadow of the bony framework of his hand on the plate．In fact, the rays could pass as easily through the fleshy part of his hand as through the black paper, but hardly at all through the bone．So Rontgen made the first X-ray picture of a hand, showing just how the bones in the hand fit together．