Page:Popular Science Monthly Volume 73.djvu/558

554

HE discovery of X-rays was announced by Professor Röntgen in December, 1895, in a communication to the Physico-medical Association of Würzburg. The date of the discovery is commonly thought to be November, 1895. As a matter of fact, the first X-ray photograph was made about two years before that time, and the accidental production of this photograph was the starting point of a series of investigations which continued for more than two years before the public announcement was made. The story was told to me by Dr. T. S. Middleton, now a physician in Chicago, who was a research student under Professor Röntgen during a period of four years, including the time when the great discovery was made.

Professor Röntgen is a man who works unceasingly as a teacher and in research, a man who brings to his students the inspiration of genius. Like Edison, he would often forget to eat were he not reminded by friends of his need of food.

He was working with cathode rays and, being an expert glass blower, prepared his own tubes. He had a habit of using his lungs as an air-pump in exhausting his tubes. Long practise had developed an athletic pair of lungs, so that he was able in this manner, aided by the increase in vacuum due to the electric discharge, to produce a vacuum sufficiently high for the production of the cathode rays. The first X-ray tube was exhausted in this way. This tube was blown to form a large bulb at the middle and bent to form a letter S at either end.

The electrodes being at the ends, the cathode rays would have to traverse the bends of the tube. Röntgen regarded the cathode rays as streams of electrified particles and believed that friction would be developed as these particles streamed past the bends of the tube. He expected this friction to result in new phenomena.

On a flat-topped desk in Professor Röntgen's private office lay an unassorted heap of books, glass tubes, photographic plate holders, platinum and aluminium electrodes, and what-not, such an unassorted heap as is likely to accumulate on the desk of a busy man. In this confusion it happened that a large book which the professor had been reading lay on a photographic plate holder. In the book lay a key serving as a bookmark. The use of a flat key as a bookmark is a