On November 8, 1895, German physicist Wilhelm Roentgen inadvertently made a significant contribution to medical science. Historical records indicate that on that day he was trying to replicate earlier experiments reported by others in which invisible cathode rays escaped from a thin aluminum window, produced a luminescent effect on fluoroscopic salts, and darkened a photographic plate. During his work, he serendipitously　noticed a faint green glow, moving like wispy clouds, near a fluorescent screen that was on a bench　several feeta　way. He concluded that a different kind of ray was mixed with the cathode rays and was amazed to find that when he 　 held materials between the cathode-ray tube and the fluorescent screen, he could see a shadow of the bones　and soft tissue in his hand as if his skin were transparent. At that moment, radiology was born. During the early part of the next century, professional organizations, such as the Radiological Society of North America (RSNA), were founded to support this new medical science.