CHAPTER XVI. The New Rays

THE NEW RAYS

IT is not given to many men to make such a wonderful discovery as fell to the lot of Professor Röntgen in the year 1895. If anyone wishes to mention something very new and wonderful, some great revelation of science during the nineteenth century, he usually puts the Röntgen Rays or X-rays in the first place. This is very natural, for these rays give men powers of vision which they could hardly expect ever to possess. They enable us to see through many dark bodies, and even through the human body itself. The discovery of these rays forms one of the most romantic chapters in the history of science.

The discovery was made in the course of some work with a vacuum tube. A vacuum tube is a bulb of glass from which all the air has been pumped. An electric lamp is a kind of vacuum tube, but it would not be suitable for the experiments of Professor Röntgen unless the filament were removed and nothing but the two platinum wires remained. If the current were sent through the bulb as usual, it would have some difficulty in passing from one platinum wire to the other, and indeed it could not pass at all unless some slight trace of air remained in the bulb.

Even then a higher pressure of electricity is required than is used for lighting the filament in the ordinary way. Instead of having the two platinum wires side by side, they are usually placed at opposite ends of the tube when the ordinary experiments with vacuum tubes are being performed. Also, instead of ending in sharp points the platinum wires usually end in small discs or caps.

When a current is sent through a tube of this kind the trace of gas in the tube shines with a strange light. The light usually shows some beautiful colours, and is arranged in layers. These layers are generally in the neighbourhood of the positive wire, which is called the anode. At the negative wire we find a layer of white, or violet, light, and next to this a dark space, which separates it from the glowing space beyond. When special care is taken to get rid of as much gas as possible, the dark space expands until it fills the whole of the tube. Then a strange thing happens. A green glow plays on the whole of the tube opposite the cathode, and it is in this green glow that the X-rays are born. But before we describe how the X-rays originate, we may say a few words of what happens in the vacuum tube, and gives rise to the green glow.

If we could see the cathode through a microscope of a magnifying power greatly beyond that of any existing microscope, we should find it to be the scene of a very intense activity. We should see great jets of small particles start from the cathode at a tremendous speed, and shoot away in straight lines until they reached the glass wall opposite, there producing the green glow. These small particles are thought to be the real particles of electricity which constitute the electric current.

An electric current consists of a stream of these extremely small particles, which are called “electrons.” They are much smaller than the atoms of a wire; and thread their way slowly between the atoms, knocking against them every now and then, and producing a great deal of heat. The same number of electrons passes through every section of the whole circuit in the same time, and naturally, when a wire in the electric circuit is very thin the electrons must pass at a greater speed in order to get through and make room for those that come after them. In a thin wire, therefore, the heat is very great, and when the wire becomes a filament, the heat is great enough to make it shine with a bright light. This gives us an electric glow-lamp.

Now, when these electrons arrive at the end of the cathode wire, they are urged strongly to cross into an open space beyond the wire, partly by the crowds of electrons following them, and partly by the strong attraction which the anode opposite exerts upon them. But the atoms of the wire themselves attract and hold the electrons, and there is therefore always some difficulty to overcome before the electrons can leave the wire. Once they are free from the cathode, they are impelled forward by the repulsion from behind and the attraction in front. Like stones falling from a great height they rush on more and more quickly.

The force which plays upon the electrons is enormously greater than the force of gravitation. It is more than a million times greater. On the other hand, the particles or electrons are very small, and, therefore, do not produce any very destructive effects, however high their speed may become. But their speed is something enormous. It is something like fifty thousand miles per second. No wonder that when these particles are stopped by a glass wall they produce some very curious effects. These effects become much more intense when they are concentrated upon a sheet of platinum placed opposite the cathode. That sheet becomes white hot and sends out the famous Röntgen Rays, which Röntgen himself called “X-rays.”

Now as to the history of the discovery of these rays. Professor Röntgen was one day experimenting with such a vacuum tube, and trying to get the electrons to go out of the tube into the open air. This experiment had been done many times before him by using a little window made of very thin aluminium, which can be penetrated by electrons.

He was studying the effect of these electrons upon a sheet of some phosphorescent substance. He wished to find out whether the electrons would still come out if the vacuum tube were enclosed completely in black cardboard. He also wished to observe the effect in complete darkness. He was surprised to find that the phosphorescent screen was lighted up, and that some influence from the vacuum tube reached the screen through the black cardboard.

Greatly struck by this observation he tried various other arrangements. He put a deal board between the tube and the screen, but found that the board made no difference whatever, and that whatever rays from the tube were lighting up the screen, these rays could pass through the deal board. He then took away the board and put in its place a thick book, but again this made no impression whatever upon the rays. Thinking that perhaps the rays were coming round to the screen in some unexplained way, he held his hand between the tube and the screen. Imagine his surprise on seeing, not the shadow of his hand, but only the shadow of the bones in his hand on the phosphorescent screen. It must have given him something of a shock, and we may suppose that he quickly turned on the light to see if his hand had really shrivelled up into a skeleton. But no, the hand looked just as usual, and yet on holding it in the path of these wonderful rays, the shadow of the bones was again distinctly visible, the flesh showing only in faint outline. It was a most wonderful discovery.

The great news was not long in travelling all over the world. The experiment was repeated thousands of times, and it was soon found out that a great new fact had been added to the range of human knowledge. It was found that metallic bodies such as coins, bullets, and needles could be located in the flesh by means of the rays playing through it on to the screen. Instead of the screen, a photographic plate could be used, and pictures of these bodies could be obtained in a few minutes.

Surgeons were not slow in using the great discovery in the hospitals, and every large hospital has had a special staff of men trained in the use of the Röntgen Rays.

But it often happens that the blessings of a new discovery are endangered by evil effects which they bring in their train, and this was very much the case with the Röntgen Rays. The men who spent all their days taking photographs by means of the new rays found to their dismay that wherever the rays played upon them for a long time the skin became dry and hot. The hair fell off, and even the nails dropped out. Worse than that, very painful sores began to appear after a time, which it was found almost impossible to heal. In some cases death was the result of prolonged exposure to the Röntgen Rays; but, as usual, science eventually succeeded in separating the good from the bad effects, and protected the skin by means of screens of lead which cannot be pierced by X-rays. Now this new great aid to surgery and medicine has been established properly and regulated satisfactorily.

The X-rays were not the only kind of new rays discovered towards the close of the nineteenth century. In fact they ushered in the discovery of quite a number of new kinds of radiation, each more wonderful than the last. We have already mentioned the green glow on the glass, and the white light on the platinum screen which catches the electrons. Somebody put forward the supposition that it is the phosphorescent light itself which sends out the X-rays. He supposed that whenever anything shines with phosphorescent light, X-rays are sent out, and these make an impression upon a photographic plate. This supposition was tested by a great Frenchman of the name of Becquerel. His father had made a great name by investigating phosphorescence, and what more natural than that the son should study the behaviour of phosphorescent bodies as regards X-rays!

But by a very extraordinary and lucky chance he chose among the many phosphorescent bodies known to him the only body that could have led him to the great new discovery which he made. That body was a substance called uranium. He exposed some crystals containing uranium to sunlight until they glowed with a thin blue light.

Then he shut up those crystals in a dark box with some photographic paper, and left them there for a few hours. At the end of that time he found that the crystals had blackened the photographic paper. This, he thought, was either the effect of the bluish light, or the effect of X-rays from the crystals. He decided to try the experiment again, but he waited in vain day after day for the sun to come out.

This, as the sequel showed, was another fortunate chance. For all this time the crystals lay ready in a drawer in the neighbourhood of a photographic plate, waiting to be exposed to the sun. Tired of waiting any longer, Becquerel thought he had better close the experiment for the present by developing the photographic plate. To his great surprise, he found that the crystals had made a strong impression upon the plate, although it had been protected by black paper, and although the crystals had not been exposed to sunlight. It then struck him that perhaps the crystals had been exposed to the sun some considerable time before, and were now only very gradually giving up the light which they had absorbed. He therefore kept them for months in complete darkness, and then exposed another plate to their action. But contrary to all expectation, he got the same result as before, so that it was clear that the action of the uranium was quite independent of light, and continued without interruption.

Even greater surprises were yet in store, for this power of uranium to give out a new kind of rays which impressed a photographic plate was found to be quite indestructible. No matter if the uranium was melted up in a crucible, pounded to a fine powder, mixed with other substances, melted or boiled, or treated with all kinds of acids, the effect was always the same so long as the quantity of uranium remained the same. The new and strange power seemed to lie in the very atoms of the uranium themselves.

This power was quite new, and therefore had to be called by a new name. The wife of another French professor of the name of Curie, who greatly distinguished herself in studying this new power, called it “radio-activity,” and this name is now used generally. Professor Curie and his wife went to a great deal of trouble to concentrate the uranium and make it as highly radio-active as they could. They found that some preparations of uranium were more active than others, and, therefore, they found that a certain sediment of the uranium ore was quite extraordinarily radio-active. They extracted this sediment from several tons of the ore.

It was an extremely expensive operation, but it was richly rewarded by another marvellous discovery, for at the end of a great deal of work they found a new substance which was a million times more radio-active than uranium. This substance they called “radium.” So intensely active was this new substance, that if shown in the dark, a small piece of it made a phosphorescent screen brightly luminous. But the radium proved as dangerous as the X-rays, for Madame Curie, who wore a small quantity of it in her sleeve, found that it gave her a sore which took several months to heal.

After the tragic death of her husband in a motor accident Madame Curie was appointed Professor of Chemistry in the Paris University, being the first lady ever appointed to such a post in that ancient city of learning.