Jackson X-ray tube, 1896.
© Science Museum / Science & Society Picture Library
This is a very early example of an X-ray tube, through which electricity was pased. It 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 pased out through the glas. 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 tisues, was a discovery which the medical profesion was keen to exploit.