Early X-ray tube, c 1896.

This early German X-ray tube is of the form originally used by Wilhelm Roentgen (1845-1923), the discoverer of X-rays, in his research. Roentgen, a German professor of physics, encountered emissions from a Crookes' discharge tube. Experiments revealed that these rays penetrated some substances more easily than others, and also fogged photographic plates. The fact that X-rays could produce images differentiating between the densities of body tissues, was a discovery which the medical profession was keen to exploit. The tube features a cup-shaped cathode which serves to focus the cathode rays onto the target (a platinum anode). When the rays hit the anode, their energy changed into invisible X-rays, which passed out through the glass.