Early radiography experiment. Historical artwork of a Ruhmkorff induction coil (left) being used to create a large electrical voltage across a Crookes tube (glass tube, upper right), a type of cathode ray tube. This sort of experiment helped to distinguish between the cathode rays (later found to be electrons) and the higher-energy X-rays produced at high voltages. Cathode rays travelled in one direction, while X-rays radiated out in all directions from their source. X-rays could also be used to image bones on photographic plates, as is being done for the hand at lower right.