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

SILVER ORNAMENT IN A BOX. CATHODOGRAPHED BY

WILLIAM JAMES MORTON. (SEE P. 130.)

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

letters more than the body of the plate. Adjoining the objects mentioned may be seen a pair of insulated wires tightly twisted together. In the ray-print the insulation is almost invisible, and the wires stand wide apart. The three irregular pieces seen near the twisted wire are coal: one piece, in the form of a wedge or prism, is of anthracite three eighths of an inch at its thickest part, and tapering to an edge; the other two are of bituminous coal varying in thickness from one sixteenth of an inch to over one fourth of an inch. The coal is relatively quite transparent, and the bituminous somewhat more so than the anthracite. The negative clearly shows by darker marks the presence of seams probably richer in earthy matter.

In this connection I make a suggestion. Instead of analyzing the coal for ash percentage, take a cathodograph of a definite thickness of it along with coals bearing known percentages of ash, and compare the shadows. At the upper left-hand corner of the photograph on this page is a small hardwood awlhandle, the awl being broken. The cathodograph shows the brass ferrule to be opaque, and shows that the wood is fairly transparent-sufficiently so to reveal the end of the broken awl above the ferrule in the wood.

Adjoining the lettered aluminium plate was placed a piece of cellulose about one thirty-second of an inch thick. It was too transparent to show in the cathodograph.

By the cellulose was a piece of bromide print in black, with white letters, «Assembly.» This was too transparent to be visible in the shadow-picture. The keyhole escutcheon seen near it is of iron, about one sixteenth of an inch thick, with chamfered edges. It is opaque, but by inspection of the negative the edges are clearly seen to transmit rays. In the upper right-hand corner of the photograph is a cork about one inch in diameter, having two glass tubes passing through it. The cork has disappeared in the shadow-picture, being too transparent. (Cathodography of corked bottles would uncork them.) The glass tubes are seen to be partly transparent.

It is indeed surprising to find the dense black coal masses transmitting the rays so freely that an inch or more in thickness would be no particular obstacle to the taking of a picture.

In developing a cathodograph picture it is noticeable that the development goes on all through the film, back as well as front. This is not the case with ordinary camera exposures, which develop from the front toward the back of the plate. The behavior noted is with the cathodograph an indication of the fact that the sensitive film itself is largely transparent to the cathode rays, and therefore lets them through without fully utilizing them. If they could all be absorbed and made to do chemical work, our time for making an impression would be much abbreviated.

To test this, I placed in front of a sensitive plate, and between it and its slide in the plateholder, four thicknesses of sensitive bromide paper. It was then placed under the Crookes tube, with a few objects-one of which was a small permanent magnet-on the cover of the plate-holder containing the plate and paper. There were thus five superposed sensitive layers traversed by the rays. A picture was obtained on each of them. These pictures were of equal intensity, and the glass had a strong impression. The indication that a dozen or twenty paper pictures might have been obtained at one time, I have since verified.

This looks as if only a small portion of the silver bromide is susceptible to these rays, and that to get the best results special preparation of the sensitive materials will be needed; or the impression may depend on fluorescence, in which case strongly fluorescent chemically inert powders should be incorporated with the sensitive substances.

There is every reason to believe that much greater speed will be attained by the use of highly sensitive materials and of greater energy in the Crookes tube apparatus.

The detection of cathode rays by fluorescence will undoubtedly be of great service in saving time in making explorations in surgery,

etc. With a highly fluorescent screen placed within the range of vision, in a dark box provided with sight-holes, the observer will be able at once to detect the presence or absence of the rays, the forms of the shadows, etc., instead of photographing them. He will be able also easily to change the direction of the rays and make observations in the different directions without loss of time.

It is possible also that an exploring apparatus, consisting of a negatively electrified body with an electroscope, may be so arranged as to give a record, or map, as it were, of the shadows cast by the cathode rays. In this case the sensitiveness can be made exceedingly great.

It is too early to settle upon any theory as to the nature of the rays. They agree in several particulars with what is called ultraviolet light, or with ultra-violet rays. Yet they are not refracted or reflected, or at least no observations have as yet been made showing that they possess the capability of refraction or reflection. Certain delicate markings which I have observed on a few cathodographs would almost indicate a trace of refraction or reflection existing; still, there may be another explanation of these markings.

May it not be that high-pitch waves in the ether, even when transverse like light-waves,

can pass between the molecules and travel in free ether between them, or otherwise undergo absorption in the molecule itself when the latter is across the path?

Be they what they may, the study of cathode rays will open up the way to further discoveries in that borderland between matter and ether. We know that magnetism concerns the ether far more than it does ordinary matter. We know that light and radiant heat are electromagnetic vibrations of high pitch in the ether. It is more than probable that gravitation is dependent on some form of ether vibration. We shall await the proof of the true nature of cathode rays, fully assured that it will come in due time.

FOR success in producing electric shadows the first requisite is a Crookes tube having a very perfect vacuum. The highest exhaustion is essential, many tubes failing from having only a sufficient vacuum to produce phosphorescence. The glass should be thin and preferably containing no lead. An ordinary Ruhmkorff coil, capable of throwing a spark four or five inches in length, suffices to stimulate the tube, provided its break works with sufficient rapidity. With the ordinary slow break very long exposures are necessary. If the bulb or tube is large, sharply defined shadows will not be obtained. The rays that produce the shadow effects do not emanate exclusively from the phosphorescent patches on the glass bulb, as Roentgen himself sup