X-Rays

or Roentgen Rays, a form of radiant energy akin to light and electricity. They were discovered in 1895-96 by Wilhelm Roentgen, at that time a professor in the University of Wurzburg. The discovery won him the Nobel prize for physics in 1901. Roentgen found that, in addition to the streamer of colored light produced by the passage of a high tension electrical current through a vacuum, other rays are produced. They cannot be seen by the eye, but they produce the same effect on a sensitive photographic plate that is produced by ordinary light. Moreover, these rays pass through aluminum and wood more readily than through glass, through flesh more readily than through bone, and through bone more readily than through lead or steel. If a hand in which a bullet or needle has lodged be interposed between the X-rays and the screen, the whole hand will cast a shadow, but the bones will cast a darker shadow than the flesh, and the bullet or needle will cast a darker shadow than the bones. In this way, the surgeon is able to locate a bullet and to examine the knitting of a fractured arm, rib, or leg. Tumors may be traced, the location of the heart noted, etc.

X-rays pass in straight lines through all substances. Thus far no way has been found of turning them from their course, or of bringing them to a focus. They have a marked physiological effect. While they cannot be seen, they yet have a certain irritating effect on the retina or else some part of the lining of the eye. It has been hoped that the rays might prove fatal to the growth of cancer and to the germs of tuberculosis. Apparent cures have been effected, but the question is still open.

X-rays afford a new test for diamonds. A genuine diamond held in the rays casts a fainter shadow than a glass imitation. X-rays appear to have a shorter wave length than light. Roentgen gave the name X-ray with reference to their unknown nature,--X being the customary algebraic symbol for the unknown. At present these rays are believed to be more nearly allied to electricity than to light.

See Crookes; Cancer; Finsen; Nobel