X Ray: In 1895, the German physicist Wilhelm Rontgen discovered that a piece of paper painted with crystals glowed when he switched on a vacuum tube.  Rontgen hypothesized that a ray coming from the tube caused this reaction.  The ray, which he called an X ray, could even penetrate a metal covering, as well as expose photographic plates.  This discovery made it possible to take photographs of bones in the body and helped doctors to diagnose illness.

The X ray tube in this picture was shipped to Dr. J. R. Welch of Spencerville, Ohio in 1932.  The tube, which was made by Westinghouse Company, Cleveland, Ohio, cost $125.