The progress of science is continually opening new fields of research and epoch-making discoveries have followed, during recent years, close one pon the other. Recently the cable from Europe brought to us the somewhat startling intelligence, that-Professor Réntgen, of Wurtzburg, had discovered a new form of radiant energy, which would penetrate opaque substances and act upon the photographic plate. Not many years back, such an announcement would have been met with doubt and derision, even by able men of science. But it is an evidence of the better knowledge and broader thought of the present day, that the brief cable message was generally accepted, by scientific men, as a precursor of an announcement of a great discovery. The lessons of the past have been well learned. And so it has proved to be. Yet, strange to say, some of the phenomena of these intangible, invisible radiations, manifestations of an unsuspected force X, had been already noticed. Professor Riintgen, however, was an_ independent discoverer and the first to make known the true character of the phenomena. He was the first to demonstrate the photographic action of the rays. It was no accidental discovery, as has been said, but the direct outcome of well conducted investigations.
Some years ago the eminent chemist and investigator, Professor William Crookes, carried out a long series of experiments in a study of the condition and action of matter ina very highly attenuated state, such as prevails within tubes from which the air or gas has been pumped out very perfectly, by means of a mercury pump. "Most readers are doubtless acquainted with the beautiful experiments showing the peculiar coloured light and fluorescence produced by the electric discharge in the so-called Geissler tubes. These are glass tubes, of rious shapes, more or less exhausted of air, sometimes containing traces of other gases, as nitrogen, hydrogen, oxygen, ete. Fine imitations of the light of the aurora Dorealis are shown by some of these tubes.
Professor Crookes, however, required, for some of his experiments, very perfect yacua, in which matter existed in the condition of the most extreme attenuation.
By means of the excellent mercury pumps now made, it is possible to reduce the tension of the gas within a tube until the pressure is measured in a few millionths of an atmosphere. Even the electric spark refuses'to pass between terminals a small fraction of an inch apart in such a vacuum. But with tubes containing a very minute residuum of attenuated matter, very strange and beautiful effects of light are produced by the electric current. An ordinary incandescent light globe, placed between the terminals of an induction coil in action, manifests a glow of light, if the vacuum ie good. It is possible that this glow will some day be utilised as a source of light. But for the satisfactory manifestations of the phenomena now under. consideration, the terminals are sealed into the glass and project within the tubes. Professor Crookes devised certain forms of tubes having terminals of dises or plates of aluminium. These are the kind most commonly used in experiments with the Réntgen rays.
Almost nothing is yet known of the physical characters of these newly discovered vibrations. The phenomena of the glow within the Crookes tubes can be studied with the eye. The molecules of highly attenuated gas are free to move over long paths of vibration without colliding with each other, as they must do under ordinary conditions of temperature and pressure. The pressure of a against, the walls of the containing vessel, is due to the impact of innumerable molecules pounding against the walls. Reduce the number of molecules by means of an air pump and the pressure due to this pounding is corres-pendingly reduced. In the Crookes tube there are comparatively few molecules and these, under the influence of the electric current, are caused to vibrate in straight lines from pole to pole, or they may be reflected from one of the aluminium terminals against the walls of the tube itself. This swinging of the molecules is manifested by lines of luminosity. Interpose a plate of metal in the path of these vibrations, it will be seen: as an impenetrable obstacle and will cast a shadow on the wall of the tube behind it. It may even become red hot by the incessant bombardment of the molecules. Certain crystals, a cole apes for example, will he made to glow, as though Some magic influence had tris: formed it into a source of wondrous light and beauty.
The light of these free-moving molecules is the so-called cathode light. The course of the vibrations can be changed by aproximating a magnet to any part of tube.
the rays may thus be deflected from their course and phenomena of great, interest and beauty invoked. But these are not graphs. The cathode ray is visible, but the rays which produce the Réntgen photo-
from it or with it, originate, in some way as yet not understood, the invisible radial tions which affect the photographic plate.
If the luminous tube is enclosed in a box of wood or of opaque paper, these invisible radiations pass through the opaque covering more readily than through glass.. A-photographic plate within its holder, held up in the darkness, in the path of the radiations, will be fogged. Some things are more transparent than others, and will cast a shadow. so that by resting a gold ring ora key on the slide of the plate holder and exposing the whole to the radiations, a shadowgraph of the articles will appear after the plate is developed in the ordinary way.
In making these shadowgraphsor x-graphs (pending further investigation the rays are designated as a-rays), it is usual to work in daylight and the tube is not enclosed in a covering. The sensitive plate is not exposed to light for the objects to be portrayed are placed upon the slide of the plate holder, which is quite transparent to the rays. - In a general way it may be stated, that metals are more opaque than wood—aluminium being quite permeable, however—flesh more transparent than bone, wood and paper the thickness of an inch or two il permit the vibrations to pass, hence it is possible to shadowgraph the bones of the hand and foot very clearly and to discover bullets embedded in the flesh, or false articulations of the joints. Mr. Edison is said to be planning to portray the human brain, perhaps hoping to discover the wheels in the brains of cranks. Anatomists and physiologists are greatly interested in the possibilities here suggested.
The presence of these radiations can be made visible to the eye. They cause a bright fluorescence with certain chemical compounds and if a paper coated with barium, platinocyanide, for example, is placed in their path, it shines in the dark,
Text read from the printed page and cleaned; old type leaves the occasional error.