Röntgen Takes an X-Ray of His Wife’s Hand

In the late autumn of 1895, Wilhelm Conrad Röntgen was working in his laboratory at the Physical Institute of the University of Würzburg, examining the effects of electric charges passed through evacuated glass tubes. He had assembled apparatus designed by contemporary investigators, including Johann Hittorf, William Crookes, and Philipp Lenard. On the afternoon of November 8, 1895, Röntgen covered a thick-walled Crookes-Hittorf tube with opaque black cardboard to block all visible light, intending to verify whether cathode rays could stimulate fluorescence through the heavier glass. After darkening the room and activating the induction coil, he observed an unexpected glimmer from a nearby bench, where a small cardboard screen coated with barium platinocyanide sat several feet away.

Repeated discharges generated the same faint luminescence, confirming to the physicist that an invisible emission was traversing the space between the tube and the coated surface. Because the emissions cast regular shadows, Röntgen concluded that they behaved as rays, yet their properties differed fundamentally from ordinary light or previously identified cathode emissions. Unable to determine their exact physical nature, he used the mathematical symbol for an unknown quantity and designated them X-rays. Over the ensuing weeks, Röntgen lived almost continuously in his workspace, methodically examining how different substances obstructed or transmitted the mysterious radiation.