Harper's Round Table, April 14, 1896

by Various

Professor Crookes, by obtaining a vastly better vacuum, obtained in these tubes some new and very interesting phenomena. As the vacuum became better and better, the light within the tubes finally disappeared, and only the inside of the glass was illuminated. This Professor Crookes explained upon the supposition that the air particles remaining in the tubes are repelled from the negative terminal or "cathode" within the tube, and shoot off from it, proceeding in straight lines, until they come into collision with other particles or with the walls of the tubes, producing light wherever the collision occurs. When the exhaustion is sufficient these particles shooting out from the cathode meet with no obstructions until they reach the walls of the tube, which are bombarded by the flying particles until they shine with a sort of phosphorescent light, while the whole interior of the tube remains dark.

FIG. 2.—A RADIOGRAPH OF A MAN'S HAND.

These experiments have been repeated again and again for the last eighteen years in scientific laboratories and lecture-rooms, always exciting the greatest interest in the wonderful phenomena disclosed. But not until recently has it been known or suspected that all the time there were proceeding from the bombarded surface other rays, incapable of exciting vision, but possessing properties, and capable of producing effects even more wonderful than any that the Crookes tube had before shown. That certain invisible rays existed in the Crookes tube radiations was known about four years ago, but it remained for Professor Röntgen to demonstrate the remarkable properties which they possess. He found that a piece of card-board painted on one side with barium platino cyanide was illuminated when held near the excited Crookes tube, and that the painted surface was equally well illuminated, whether it or the reverse side of the card-board was presented to the tube. He further found that when the whole tube was covered with black paper, so that no rays affecting the eye could emerge, the painted screen was still illuminated, and further yet, that the illumination remained visible when a board an inch thick, a book of a thousand pages, or a plate of hard rubber was interposed between the tube and screen.

On the contrary, he found that glass, thin pieces of metal, the bones of the hand, more or less stopped the rays, and so cast shadows. It must have been a startling image that met Professor Röntgen's eye when first he placed his hand in the path of the rays, and saw upon the screen a bony skeleton hand with only a faint outline of flesh and cartilage. It was a startling experiment to me, after I had read all the accounts of Professor Röntgen's work, and knew what to expect, when I first saw the shadow of my own hand upon the fluorescent screen. Fig. 2 shows the appearance of such a shadow. After demonstrating in this way the transmission powers of various substances, Professor Röntgen tried the effect of the rays upon the photographic plate, and found it possible to fix there the images that he had seen upon the fluorescent screen.

Fig. 1 will show how the results are obtained. A is a galvanic battery, B is a Ruhmkorff induction coil, C is a Crookes tube, and D is the plate-holder containing the sensitive plate.

FIG. 3.—A GOLDFISH WITH THE SPINE AND SOME OF THE INTERNAL ORGANS VISIBLE.

The battery produces a low-tension harmless current that is rapidly closed and broken at the induction coil, which transforms it into a high-tension current capable of producing electric sparks, and giving exceedingly painful if not fatal electric shocks. Wires convey this high-tension current from the coil to the terminals of the Crookes tube, where the Röntgen rays are produced whenever the current is turned on. In the figure the plate-holder is shown only a few inches from the tube, where the effect of the rays is strong.

Fig. 3 shows a goldfish, with all his scales and flesh on. The line of his spine is clearly visible, and many of the inner organs of his body can be clearly seen, and the skeleton comes out very clearly, because the bones are more opaque to these rays than is any other part of the body.