The vacuum chamber consisted of a glass cylinder three feet long and about eight inches in diameter. The two ends were closed by sheets of aluminum, and it could be exhausted through a side tube. The reader will immediately ask, in view of what has been said, How could the glass tube be hermetically closed with sheets of aluminum? This was indeed a difficult matter, but less difficult than in the case of the Crooke’s tube, for the ends of the glass cylinder were provided with heavy brass flanges, which were perfectly flat, and the sheets of aluminum lying smoothly could be confined by many bolts between the flange and suitable brass heads. This cylinder, having been exhausted, was placed between the Crooke’s tube and the arm, for instance, in the hope that a greater depth of human flesh and tissue might be penetrated by the rays. It was speedily seen that the absorption of the layer of air three feet thick could not be detected either by photographs or the fluorescent screen. The glass cylinder was then filled with rarefied hydrogen, but no advantage was apparent. If the photographs of the human hand were taken, one through the rarefied cylinder and the other through an equivalent thickness of air, no difference in clearness or depth of definition could be perceived. The amount of absorption by a column of air three feet in length is less than ten per cent. This result interested me greatly, for it shows the remarkable difference between the X rays and the cathode rays, which had been investigated by Crooke, Hittorf, and Lenard; for the cathode rays are greatly absorbed by atmospheric air, being reduced in passing through five or six inches of air to one four-hundredth part of their value.
The small amount of absorption of the X rays lifts them into the realm of very short wave lengths of light, for their behavior in regard to the absorption by air is very analogous to that of ultra-violet rays. Although the vacuum chamber, by which I looked, showed no absorption of the X rays, it disclosed a beautiful phenomenon. In a dark room this large tube, three feet long and eight inches wide, was filled with a roseate light, which wavered like the northern lights when the Crooke’s tube was emitting the X rays. If the finger was brought near the glass walls of the cylinder a stream of light apparently emanated from a point on the inside wall of the cylinder. The hand thus had ghostly streamers giving an image of it, although the hand itself was invisible. These banners of light could be diverted in any direction by the hand or by any conducting body brought near, and gave a vivid conception of how the streaming of the aurora can be brought about by this flitting of conducting clouds or the drifting of moisture-laden strata of air below the rarefied space in which the beams of the northern light dart back and forth. Both in the case of the Crooke’s tube and the aurora these streamers are produced by electrical discharges through rarefied air. The experiments show that outside the Crooke’s tube there is a strong electrical attraction and repulsion, which is only revealed in darkness and in a cold, lifeless, airless space, such as exists between us and the sun. Can we not extend our thoughts from the contemplation of this laboratory experiment to that of the immensely greater play of electrical forces between the earth and the sun across the immense vacant space ninety millions of miles in distance?
The mysterious effects of the X rays on the molecules in the air form a great subject of inquiry, and the investigation of it promises to extend our knowledge of electricity and light and heat. When the Crooke’s tube is excited we are conscious of a mysterious activity within it, for its glass walls glow with a phosphorescent light, and if certain crystals, like the diamond or the ruby, are placed in the tube, this phosphorescent light is vivid. Outside the tube, in free air, these luminescent effects are also present. The air is under an electrical strain, which is shown by the auroral streamers when this air is rarefied, and an electrical charge can not be maintained on a pith ball—it is dissipated in some strange manner. Still stranger, an electrical current is greatly aided by the X rays in its endeavor to pass through air—they make for the time being air a conductor. Furthermore, these rays separate the air into positively laden and negatively laden particles.
The electrical discharge in the Crooke’s tube is many-sided in its manifestations. Its energy seems all-pervading in the room where it occurs. Before the discharge passes through the rarefied space in the tube its energy manifests itself by a crackling spark, a miniature lightning discharge. This spark, five or six inches in length, can send out magnetic waves which extend far beyond the narrow limits of the room. They can be detected, by the methods of wireless telegraphy, fifty miles. When the same amount of energy is developed in a Crooke’s tube the magnetic waves hardly pass beyond the walls of the room, and the phenomenon of phosphorescence and fluorescence and the strange molecular effects outside the Crooke’s tube spring into prominence. The crackling spark outside the tube is far-reaching in its effect, yet it shows no signs of the X rays, its light can not penetrate the human body, it excites only a feeble phosphorescence at a distance of even two or three feet, while the same energy excited in the Crooke’s tube can cause luminescence at a distance of twenty feet. The crackling spark, however, can be seen much farther than the light of the Crooke’s tube, and it can also impress a photographic plate at much greater distance. The following experiments will illustrate the different manifestations of energy of which an electrical discharge is capable. I produced an electrical spark about six inches in length and exposed a photographic plate for six seconds, at a distance of two, ten, and twenty feet, to its light. A thin strip of tin, with a circular hole cut in it, served as a shutter. The sensitive plate was thus protected, except in front of this aperture. The images exhibit the decrease in light with the increase of distance. Another portion of the sensitive plate was exposed in the same manner during the same length of time to the light of a Crooke’s tube which was excited by this same spark. No image was obtained at a distance of ten feet, and barely one at three feet. The spark in air, therefore, was far more energetic photographically than the X rays, but it could not penetrate solid materials. This property was given to it by its passage through rarefied space. I then covered a screen with a phosphorescent substance, and exposed it to the spark in air. The phosphorescent light could barely be detected at a distance of three feet, while with a spark in rarefied air it could be seen at a distance of twenty feet.
When we consider these experiments we see that the X rays act toward phosphorescent matter much as the spark in air behaves toward the photographic plate. Now, these results, taken in connection with the strong electrical effects in the neighborhood of an excited Crooke’s tube, points to a certain connection between phosphorescence and electricity. Can it be that the strange light is excited by very short electrical waves sent out from the tube, which can not travel far but are very active in producing molecular effects? This activity, indeed, may prevent their extending to great distances. Wireless telegraphy evidently depends upon one set of waves sent out by a spark, and X-ray photographs upon another set developed only in rarefied air. Phosphorescence can not be produced with ease by the spark in air. On the contrary, it is developed to a remarkable degree and at comparatively great distances by the discharge in rarefied air. It has been shown by Mr. Burbank and myself that electrical force can develop phosphorescent light in certain crystals. The sunlight can do the same. Is sunlight an electrical phenomenon? That it is constitutes the greatest hypothesis in physics of this century. When we reflect, too, that the phosphorescence of the firefly is excited by some manifestation of a living organism—nerve force or some related force—shall we not include nerve force in the electrical category?
The X rays, therefore, bring into prominence strange lights which had heretofore been noticed chiefly by keen-eyed investigators, and which, with their names, phosphorescence and fluorescence, were unknown to the bulk of mankind. The fluorescent screen, by means of which surgeons observe the skeleton of the body, has now taken its place in medical practice with the stethoscope, by which the mechanism of the lungs is studied, and hopes have been excited that the blind may yet use the X rays in detecting objects and in regaining a sense of vision, even though this sense may be only partial. It is a curious fact that the retina of the eye is phosphorescent and fluorescent, and that one can see the shadow of certain objects in the dark when one stands so that the feeble X rays fall upon the eye. In other words, the retina acts as a fluorescent screen. The eye at present recognizes only a limited number of the waves that are surging about us. We can see the colors from red to violet, but the dark colors, so to speak, formed by waves longer than 1/40000 of an inch and shorter than 1/100000 of an inch make no recognizable impress upon our retina, unless, indeed, they constitute telepathic signals which apparently stir our consciousness and make us believe that friends are communicating from a distance. The electrical discharge has lifted, so to speak, a realm of short waves of energy out of the darkness and made them visible. Can the human brain be made conscious of other waves which fill space?
But we have not by any means exhausted the protean manifestations of the X rays. Besides the photographic, the phosphorescent, and fluorescent effects, there are still more singular properties of these rays. One of the most striking consists in their opening a path for a current of electricity. The electrical discharge, feeble in itself, not capable of lifting by means of a motor a pound weight a foot from the floor, is yet competent to open a path for a current which can set all the trolley cars of a great city in motion. To exhibit this mysterious effect we bring the ends of the electrical current which we wish to excite near each other, but not touching, in a glass tube with thin walls, from which the air has been exhausted. When the X rays fall on the gap between the wires the electrical current immediately jumps across the gap with a vivid light. We have here the mechanism of an electrical relay—the feeble energy of the electric discharge can call into play a giant energy. By what energy does it accomplish this? Is it by compelling molecules to put themselves in line, so that the electrical current can bridge the gap? Is it by breaking down this mysterious ether of space, as if we threw a stone at a turbid bull’s eye in a prison chamber and let in a flood of sunlight? How the imagination is stirred by this process, what seems dead and lifeless can, by a physical agency, be stirred to endless activity! The rays are like the touch of Ithuriel’s spear.
The electrical discharge can accomplish all this, but the story of its activity is not yet told. It can not be told, for each year adds information in regard to these activities, for there are thousands of investigators at work. Another far-reaching manifestation is this: the rays can separate the air or a gas into its constituent particles, much as a strong electrical current separates water into oxygen and hydrogen. They can communicate electrical charges to these particles—positive and negative charges. The charged air-particles, when forced through partitions of spun glass, does not give up their electricity as they do when they are charged by an electrical machine. This curious manifestation leads me to suspect that the electricity and magnetism of the earth may be caused by an X-ray effect on our atmosphere. The sun and the earth are separated like the terminals of a Crooke’s tube—two conductors with a vacuum between. An electrical excitation from the sun may cause an electrical discharge between it and the earth. This discharge might consist of an X-ray effect which could separate the upper layers of the atmosphere into positive and negative charges. The velocity of the negatively charged particles is greater than that of the positively charged ones, and the revolution of the earth may cause such a movement of these electrified particles that electrical currents may be generated which in circulation around the earth could produce the observed magnetism of the north and south poles, together with the auroral lights characteristic of those regions. This, I am well aware, is an audacious theory. It is certainly a vast extension of the laboratory experiments I have described, but the electrical radiations developed in electrical discharges are as competent to produce powerful magnetic whirls as the heat radiations in our atmosphere to develop cyclones. In the lower regions of our atmosphere the air is an insulator like glass to the passage of an electrical current. A layer a foot thick can prevent the circulation of the most powerful current which is now used to generate horse power. When this air space is rarefied at a certain degree of rarefaction the electrical current passes, especially, as we have seen, if it is illuminated by the X rays. When, therefore, we ascend to a height of ten or twenty miles the rarefied air becomes an excellent conductor of electricity of high electro-motive force. To my mind the conditions exist for developing an electrical state in the earth’s covering of air, which is competent to explain the electrical manifestations of the air, the auroral gleam, and the mysterious effect on the magnetic needle which keeps it directed to the magnetic north. Can not we conclude that the study of the X rays bids fair to greatly extend our conceptions of the constitution of matter and of the action and interaction of Nature’s forces?
A Himalayan explorer reported, a few years ago, that he had seen, from one of the lofty summits of the Mount Everest district, a peak which, beheld in the same view with Mount Everest, was evidently higher than it. Nothing has been heard of the matter since then till the recent appearance of Major L. A. Waddell’s book, Among the Himalayas. This author, who has explored the same region, represents that the Tibetans there say there is another mountain, due north of Mount Everest, that exceeds that peak in height, thus confirming the story of the former Alpinist. It appears that Mount Everest is not called Gaurisankar or Deodunga, as some affirm, but that the Tibetan name of the culminating peak of the group is Jomokang-kar—“The Lady White Glacier.”