tubes, and by his brilliant demonstrations in them of matter in the fourth, or «radiant,» state, of which Faraday spoke eighty years From these experiments by Crookes dated new phenomena of phosphorescence

fluence, but they refuse to be reflected, and go through various prisms without any sort of apparent refraction. They persist in following absolutely straight lines, starting from the point on the glass bulb that is seen to be faintly fluorescing with a blue-green light, under the action of the invisible rays from the cathode to the glass. While they present analogies with the ultra-violet rays of the spectrum, their close identity with light is still regarded as doubtful. Light is attributed to transverse vibrations of the ether, but Professor Roentgen has suggested that his rays. may be longitudinal vibrations, like soundpulses in the air. They do at least throw shadows, cause chemical action, and set up fluorescence, while the last fact would obviously suggest that they may engender heat.

IN THE CHEMICAL DEPARTMENT, U. S. MILITARY
ACADEMY, WEST POINT, N. Y.

and fluorescence created by electric action. When the current is passed into a vacuum-tube which has wires or disks sealed into each end or side walls, the glow, starting from the positive, or anode, tip, fades out as it approaches the negative, or cathode, end. Around the cathode exists a dark space, a little No Ray Land, or buffer state, at the outer edge of which the deep violet radiations utterly die out. Just what the conditions are, and just what happens in the dark cathode region, seems uncertain, but the subject has been deeply investigated, and Professor Roentgen's discovery is one fruit of exploration in that mysterious auroral territory.

It was first pointed out by the late Professor Hertz of Germany that these ultra-violet rays from the cathode could penetrate opaque bodies, such as aluminium, in a vacuum. This was interesting, but Dr. Philip Lenard further showed that such rays would also pass out into the air and through any substance lying beyond the vacuum. They would travel a considerable distance, would cause phosphorescence, and would act on photographic plates. From this to the discovery of Roentgen, who has caused the permeable substances interposed in the lines of these rays to register their shadows on a photographic plate, is but a step, though a long and memorable one.

At this moment discussion is rife as to the nature of the Roentgen ray, and many old theories as to light, electricity, and the ether are threatened with change. The obedience of the ordinary cathode rays to a magnet is one of their characteristics; but the X rays are still Bezonians whose king is unknown, for they not only do not respond to magnetic in

VOL. LII.-16.

peculiarly irritating to the eye, and others have been making suggestive experiments to prove the similarity of these subtle emanations with non-luminous ultra-violet portions of the spectrum, to which the word «light » is not usually applied.

The electrical conditions involved are of interest by themselves, and hence the energy of investigation is now concentrating upon them. The most striking of the new results is that announced by Professor J. J. Thomson, who discovers that the Roentgen rays dissipate the electrostatic charge of any substance upon which they fall, no matter how the body may be protected against discharge. From this the writer would infer that the Roentgen rays are those which, on emerging from their prison of glass or aluminium, have lost their own electric charge, perhaps entirely. Professor Thomson states, moreover, that the nature of the charge, whether posi

tive or negative, is immaterial. The corollary drawn by him from this is that all bodies under the influence of these rays become conductors. One such fact indicates many possibilities in the electrical arts and sciences. There is no need now to dwell upon the value of the Roentgen rays in surgery and dentistry, for the newspaper press of Europe and America has been full of their use in revealing the condition of the bony structure of the body. Their employment in the testing of metals, the inspection of objects in closed or concealed packages, and the detection of differences in various substances, is obvious. One immediate and important application already made on both sides of the Atlantic is to the study of moving objects projected on a fluorescent screen, while yet another invention is aimed at seeing and photographing objects hidden by darkness.

It will conduce much to the utility of these rays, however, to determine, first of all, their nature; that is, whether they are simply streams of matter under electrical impulse, or light of short wave-length, or some new phenomenon of vibration in the ether itself.

Thomas Commerford Martin.

EDITOR OF THE ELECTRICAL ENGINEER.»

ing the high-tension electricity necessary for its excitation. At the start the bulb is full of air, and as soon as the coil is set in action crooked blue sparks pass freely between the aluminium plates within. The pump is now used, the silvery fluid alternately rising and falling within its tubes, and driving out the air before it. With its first stroke we observe a change in the bulb. The blue sparks cease, and in their place appears a waving purple flame, which, as the air becomes rarer, broadens, and finally breaks up into stratifications. The room is now darkened. Little disks of bluishwhite light fill the tube, resembling somewhat a pile of saucers. The spaces between them widen, and finally a dark space appears about one of the electrodes. The discharge is now approaching the form described by Crookes as «radiant,» the light becomes fainter, and the dark space widens out until it touches the glass wall, which instantly glows with its characteristic green phosphorescence. A few more strokes of the pump and the vacuum is practically perfect. The resistance to the passage of the current is now so great, and the potential on the wires rises to such a point, that purple fringes of electric fire spring forth into the air. Sparks occasionally leap about the outside of the bulb, preferring the

A LIVE MOUSE. (UNDER CHLOROFORM.) On entering the room in which are arranged the elaborate paraphernalia necessary for the production of the Roentgen phenomena, the self-acting mercurial air-pump, with its labyrinth of tubes and bulbs, is the first object that attracts notice. Connected with this by a slender tube is the small glass bulb, with its two electrodes of aluminium, which is the source of the new energy; while just below it is the huge Ruhmkorff induction-coil, furnish

long air-gap to the shorter but vacuous one within. The entire inner surface shines with a pale emerald light, while directly in front of one of the disks is a very bright spot of a yellowish color, where the full force of the cathode rays falls. This spot is the source of the mysterious «X rays,» which, though unseen, radiate from it in all directions like light.

The bulb is now covered with a thick black

and we see a shadow of the plate with its stenciled word. A wooden box of lead-pencils shows only the shadows of the leads as a number of narrow parallel lines. And now comes the most startling experiment of all. We hold our hand behind the screen, and, closely observing the luminous surface, perceive within the dim outlines of the flesh the sharp and distinct image of its skeleton. Every bone is

perfect, even the cartilaginous spaces between being discernible. It is impossible to describe the feeling of awe that one experiences on actually seeing the image of his own skeleton within the enshrouding flesh.

Wonderful as are these phosphorescent pictures, even more so are the photographic images. The X rays, though making no impression on the eye, exert a very powerful

action on the photographic plate. It is this property which renders the discovery of such value; for in place of the transient shadows on the luminous screen, sharp and clear photographs can be made, which may be examined at leisure. These photographs can be taken in broad daylight. The plate, protected from light by a holder of the usual kind or by several thicknesses of black paper, is placed at a distance of eighteen or twenty inches from the vacuum-tube, and the object to be photographed is laid upon it. The photograph of the human hand which appears on page 123 was made by the writer with the apparatus of the Berlin Physical Institute. The seal-ring on the little finger shows the opacity of the heavy metals to the rays, its image being much darker than that of the bones. In taking this picture the hand was placed near the exhausted tube, which was directly over the little finger; here the rays fell perpendicularly, while those that cast the shadows of the other fingers struck the plate in an oblique direction, which caused a slight distortion or broadening of the image. The photograph of a bird was made by Herr Klingenberg in the laboratory of the Technical High School in Charlottenburg. One of the legs was broken, and the position of the splintered ends is distinctly shown in the picture. The dislocation of the vertebræ in the neck, caused probably by wringing, is also noticeable.

The other picture illustrating this note was taken by Dr. Kaufman in the physical laboratory of the University of Berlin, and shows the anatomy of a living but chloroformed mouse. This is perhaps the most interesting of all. Beginning with the head, we see within the outline of the creature's profile the sharp contours of the skull and teeth. A trace appears of the thin, delicate ears. Just behind the skull are the almost transparent shoulderblades, in shape not unlike the wings of a bee. Through the ribs we discern an almost white area, the lungs, which, being filled with air and of trifling density, allow the rays to pass. Just in front of and below this white patch is seen the faint outline of the heart. Even the tendons of the hind legs appear, and the entire skeleton stands out almost as clearly as if the flesh had been removed.

outside foils of a pair of Leyden jars, the knobs of which were connected with the terminals of the machine respectively, discharges at the rate of about thirty per minute taking place between the separated terminals.

The sensitive plate (5X7) was placed in a pasteboard box, face up, and had a sheet of black paper wrapped about it. It was thus shielded by a layer of paper and another of pasteboard. Just above the plate, and on the top of the box, were laid a variety of objects; and above them, at a distance of about four inches, was the under side of the Crookes tube. An ordinary photograph of the objects was taken by the camera, a print of which is shown on the following page. It shows several things which do not appear in the cathodograph, the reason being that they were practically transparent. Near the center is a small brass gearwheel which is quite opaque; it was one eighth of an inch thick, except the hub, which gave a full thickness of one fourth of an inch. Near the brass wheel is a small sea-urchin, the structure of which is partly calcareous. The rays have gone through and revealed a portion of the interior structure. Likewise, the rays have passed through a small starfish

and rendered considerable detail, which is better distinguished in the negative than in the print. By the starfish was a piece of white paper with a collection of blue-black crystals of siliccn. These are too transparent to show in the ray-print. Adjoining the wheel and the sea-urchin is a plate of aluminium about three sixty-fourths of an inch thick, having letters stamped into it. The stamp depressions go about half-way through. The whole plate is seen to be partly transparent as compared with the brass wheel, and the