THE RÖNTGEN RAYS IN AMERICA.
By Cleveland Moffett.
AT the top of the great Sloane laboratory of Yale University, in an experimenting room lined with curious apparatus, I found Professor Arthur W. Wright experimenting with the wonderful Röntgen rays. Professor Wright, a small, low-voiced man, of modest manner, has achieved, in his experiments in photographing through solid substances, some of the most interesting and remarkable results thus far attained in this country. His success is, no doubt, largely due to the fact that for years he had been experimenting constantly with vacuum tubes similar to the Crookes tubes used in producing the cathode rays.
When I arrived, Professor Wright was at work with a Crookes tube, nearly spherical in shape, and about five inches in diameter—the one with which he has taken all his shadow pictures. His best results have been obtained with long exposures—an hour or an hour and a half—and he regards it as of the first importance that the objects through which the Röntgen rays are to be projected be placed as near as possible to the sensitized plate.
It is from a failure to observe this precaution that so many of the shadow pictures show blurred outlines. It is with these pictures as with a shadow of the hand thrown on the wall—the nearer the hand is to the wall, the more distinct becomes the shadow; and this consideration makes Professor Wright doubt whether it will be possible, with the present facilities, to get clearly cut shadow images of very thick objects, or in cases where the pictures are taken through a thick board or other obstacle. The Röntgen rays will doubtless traverse the board, and shadows will be formed upon the plate, but there will be an uncertainty or dimness of outline that will render the results unsatisfactory. It is for this reason that Professor Wright has taken most of his shadow pictures through only the thickness of ebonite in his plate-holder. A most successful shadow picture taken by Professor Wright in this way, shows five objects laid side by side on a large plate—a saw, a case of pocket tools in their cover, a pocket lense opened out as for use, a pair of eye-glasses inside their leather case, and an awl. As will be seen from the accompanying reproduction of this picture, all the objects are photographed with remarkable distinctness, the leather case of the eye-glasses being almost transparent, the wood of the handles of the awl and saw being a little less so, while the glass in the eye-glasses is less transparent than either. In the case of the awl and the saw, the iron stem of the tool shows plainly inside the wooden handle. This photograph is similar to a dozen that have been taken by Professor Wright with equal success. The exposure here was fifty-five minutes.
A more remarkable picture is one taken in the same way, but with a somewhat longer exposure—of a rabbit laid upon the ebonite plate, and so successfully pierced with the Röntgen rays that not only the bones of the body show plainly, but also the six grains of shot with which the animal was killed. The bones of the fore legs show with beautiful distinctness inside the shadowy flesh, while a closer inspection makes visible the ribs, the cartilages of the ear, and a lighter region in the centre of the body, which marks the location of the heart.
Like most experimenters, Professor Wright has taken numerous shadow pictures of the human hand, showing the bones within, and he has made a great number of experiments in photographing various metals and different varieties of quartz and glass, with a view to studying characteristic differences in the shadows produced. A photograph of the latter sort is reproduced on page 401. Aluminium shows a remarkable degree of transparency to the Röntgen rays; so much so that Professor Wright was able to photograph a medal of this metal, showing in the same picture the designs and lettering on both sides of the medal, presented simultaneously in superimposed images. The denser metals, however, give in the main black shadows, which offer little opportunity of distinguishing between them.
As to the nature of the Röntgen rays, Professor Wright is inclined to regard them as a mode of motion through the ether, in longitudinal stresses; and he thinks that, while they are in many ways similar to the rays discovered by Lenard a year or so ago, they still present important characteristics of their own. It may be, he thinks, that the Röntgen rays are the ordinary cathode rays produced in a Crookes tube, filtered, if one may so express it, of the metallic particles carried in their electrical stream from the metal terminal, on passing through the glass. It is well known that the metal terminals of a Crookes tube are steadily worn away while the current is passing; so much so that sometimes portions of the interior of the tube become coated with a metallic deposit almost mirror-like.
As to the future, Professor Wright feels convinced that important results will be achieved in surgery and medicine by the use of these new rays, while in physical science they point to an entirely new field of investigation. The most necessary thing now is to find some means of producing streams of Röntgen rays of greater volume and intensity, so as to make possible greater penetration and distinctness in the images. Thus far only small Crookes tubes have been used, and much is to be expected when larger ones become available; but there is great difficulty in the manufacture of them. It might be possible, Professor Wright thinks, to get good results by using, instead of the Crookes tube, a large sphere of aluminium, which is more transparent to the new rays than glass and possesses considerable strength. It is a delicate question, however, whether the increased thickness of metal necessary to resist the air pressure upon a vacuum would not offset the advantage gained from the greater size. Moreover, it is a matter for experiment still to determine, what kind of an electric current would be necessary to excite such a larger tube with the best results.
Among the most important experiments in shadow photography made thus far in America are those of Dr. William J. Morton of New York, who was the first in this country to use the disruptive discharges of static electricity in connection with the Röntgen discovery, and to demonstrate that shadow pictures may be successfully taken without the use of Crookes tubes. It was the well-known photographic properties of ordinary lightning that made Dr. Morton suspect that cathode rays are produced freely in the air when there is an electric discharge from the heavens. Reasoning thus, he resolved to search for cathode rays in the ten-inch lightning flash he was able to produce between the poles of his immense Holtz machine, probably the largest in this country.
On January 30th he suspended a glass plate, with a circular window in the middle, between the two poles. Cemented to this plate of glass was one of hard rubber, about equal in size, which of course covered the window in the glass. Back of the rubber plate was suspended a photographic plate in the plate-holder, and outside of this, between it and the rubber surface, were ten letters cut from thin copper. Dr. Morton proposed to see if he could not prove the existence of cathode rays between the poles by causing them to picture in shadow, upon the sensitized plate, the letters thus exposed.
In order to do this it was necessary to separate the ordinary electric sparks from the invisible cathode rays which, as Dr. Morton believed, accompanied them. It was to accomplish this that he used the double plates of glass and hard rubber placed, as already described, between the two poles; for while the ordinary electric spark would not traverse the rubber, any cathode rays that might be present would do so with great ease, the circular window in the glass plate allowing them passage there.
DR. WILLIAM J. MORTON PHOTOGRAPHING HIS OWN HAND UNDER RÖNTGEN RAYS.
In this case the vacuum bulb is charged from Leyden jars which, in their turn, are excited by an induction coil.
The current being turned on, it was found that the powerful electric sparks visible to the eye, unable to follow a straight course on account of the intervening rubber plate, jumped around the two plates in jagged, lightning-like lines, and thus reached the other pole of the machine. But it was noticed that at the same time a faint spray of purplish light was streaming straight through the rubber between the two holes, as if its passage was not interfered with by the rubber plate. It was in company with this stream of violet rays, known as the brush discharge, that the doctor conceived the invisible Röntgen rays to be projected at each spark discharge around the plate; and presently, when the photographic plate was developed, it was found that his conception was based on fact. For there, dim in outline, but unmistakable, were shadow pictures of the ten letters which stand as historic, since they were probably the first shadow pictures in the world taken without any bulb or vacuum tube whatever. These shadow pictures Dr. Morton carefully distinguished from the ordinary blackening effects on the film produced by electrified objects.
Pursuing his experiments with static electricity, Dr. Morton soon found that better results could be obtained by the use of Leyden jars influenced by the Holtz machine, and discharging into a vacuum bulb, as shown in the illustration on this page. This arrangement of the apparatus has the advantage of making it much easier to regulate the electric supply and to modify its intensity, and Dr. Morton finds that in this way large vacuum tubes, perhaps twenty inches in diameter, may be excited to the point of doing practical work without danger of breaking the glass walls. But certain precautions are necessary. When he uses tin-foil electrodes on the outside of the bulb, he protects the tin-foil edges, and, what is more essential, uses extremely small Leyden jars and a short spark gap between the poles of the discharging rods. The philosophy of this is, that the smaller the jars, the greater their number of oscillations per second (easily fifteen million, according to Dr. Lodge's computations), the shorter the wave length, and, therefore, the greater the intensity of effects.
A GROUP OF FAMILIAR ARTICLES UNDER THE RÖNTGEN RAYS.
From a photograph by Professor Arthur W. Wright of Yale College, taken through an ebonite plate-holder with fifty-five minutes exposure. It shows a pair of spectacles in their leather case; an awl and a saw, with the iron stem, plainly visible through the wooden handles; a magnifying-glass; and a combination wooden tool-handle with metallic tools stored in the head, and the metallic clamp visible through the lower half.
The next step was to bring more energy into play, still using Leyden jars; and for this purpose Dr. Morton placed within the circuit between the jars a Tesla oscillating coil. He was thus able to use in his shadow pictures the most powerful sparks the machine was capable of producing (twelve inches), sending the Leyden-jar discharge through the primary of the coil, and employing for the excitation of the vacuum tube the "step up" current of the secondary coil with a potential incalculably increased.
While Dr. Morton has in some of his experiments excited his Leyden jars from an induction coil, he thinks the best promise lies in the use of powerful Holtz machines; and he now uses no Leyden jars or converters, thus greatly adding to the simplicity of operations.
In regard to the bulb, Dr. Morton has tested various kinds of vacuum tubes, the ordinary Crookes tubes, the Geissler tubes, and has obtained excellent results from the use of a special vacuum lamp adapted by himself to the purpose. One of his ingenious expedients was to turn to use an ordinary radiometer of large bulb, and, having fitted this with tin-foil electrodes, he found that he was able to get strongly marked shadow pictures. This application of the Röntgen principle will commend itself to many students who, being unable to provide themselves with the rare and expensive Crookes tubes, may buy a radiometer which will serve their purpose excellently in any laboratory supply store, the cost being only a few dollars, while the application of the tin foil electrodes is perfectly simple.
In the-well equipped Jackson laboratory at Trinity College, Hartford, I found Dr. W.L. Robb, the professor of physics, surrounded by enthusiastic students, who were assisting him in some experiments with the new rays. Dr. Robb is the better qualified for this work from the fact that he pursued his electrical studies at the Würzburg University, in the very laboratory where Professor Röntgen made his great discovery. The picture reproduced herewith, showing a human foot inside the shoe, was taken by Dr. Robb. The Crookes tubes used in this and in most of Dr. Robb's experiments are considerably larger than any I have seen elsewhere, being pear-shaped, about eight inches long, and four inches wide at the widest part. It is, perhaps, to the excellence of this tube that Dr. Robb owes part of his success. At any rate, in the foot picture the bones are outlined through shoe and stocking, while every nail in the sole of the shoe shows plainly, although the rays came from above, striking the top of the foot first, the sole resting upon the plate-holder. In other of Dr. Robb's pictures equally fine results were obtained; notably in one of a fish, reproduced herewith, and showing the bony structure of the body; one of a razor, where the lighter shadow proves that the hollow ground portion is almost as thin as the edge; and one of a man's hand, taken for use in a lawsuit, to prove that the bones of the thumb, which had been crushed and broken in an accident, had been improperly set by the attending physician.
THOMAS A. EDISON EXPERIMENTING WITH THE
RÖNTGEN RAYS.
Dr. Robb has made a series of novel and important experiments with tubes from which the air has been exhausted in varying degrees, and has concluded from these that it is impossible to produce the Röntgen phenomena unless there is present in the tube an almost perfect vacuum. Through a tube half exhausted, on connecting it with an induction coil, he obtained merely the ordinary series of sparks; in a tube three-quarters exhausted, he obtained a reddish glow from end to end, a torpedo-shaped stream of fire; through a tube exhausted to a fairly high degree—what the electric companies would call "not bad"—he obtained a beautiful steaked effect of bluish striæ in transverse layers. Finally, in a tube exhausted as highly as possible, he obtained a faint fluorescent glow, like that produced in a Crookes tube. This fluorescence of the glass, according to Dr. Robb, invariably accompanies the discharge of Röntgen rays, and it is likely that these rays are produced more abundantly as the fluorescence increases. Just how perfect a vacuum is needed to give the best results remains a matter of conjecture. It is possible, of course, as Tesla believes, that with an absolutely perfect vacuum no results whatever would be obtained.
Dr. Robb has discovered that in order to get the best results with shadow pictures it is necessary to use special developers for the plates, and a different process in the dark-room from the one known to ordinary photographers. In a general way, it is necessary to use solutions designed to affect the ultra-violet rays, and not the visible rays of the spectrum. Having succeeded, after much experiment, in thus modifying his developing process to meet the needs of the case, Dr. Robb finds that he makes a great gain in time of exposure, fifteen minutes being sufficient for the average shadow picture taken through a layer of wood or leather, and half an hour representing an extreme case. In some shadow pictures, as, for instance, in taking a lead-pencil, it is a great mistake to give an exposure exceeding two or three minutes; for the wood is so transparent that with a long exposure it does not show at all, and the effect of the picture is spoiled. Indeed, Dr. Robb finds that there is a constant tendency to shorten the time of exposure, and with good results. For instance, one of the best shadow pictures he had taken was of a box of instruments covered by two thicknesses of leather, two thicknesses of velvet, and two thicknesses of wood; and yet the time of exposure, owing to an accident to the coil, was only five minutes.
Dr. Robb made one very interesting experiment a few days ago in the interest of a large bicycle company which sent to him specimens of carbon steel and nickel steel for the purpose of having him test them with the Röntgen rays, and see if they showed any radical differences in the crystalline structure. Photographs were taken as desired, but at the time of my visit only negative results had been obtained.
Dr. Robb realizes the great desirability of finding a stronger source of Röntgen rays, and has himself begun experimenting with exhaustive bulbs made of aluminium. One of these he has already finished, and has obtained some results with it, but not such as are entirely satisfactory, owing to the great difficulty in obtaining a high vacuum without special facilities.
I also visited Professor U.I. Pupin of Columbia College, who has been making numerous experiments with the Röntgen rays, and has produced at least one very remarkable shadow picture. This is of the hand of a gentleman resident in New York, who, while on a hunting trip in England a few months ago, was so unfortunate as to discharge his gun into his right hand, no less than forty shot lodging in the palm and fingers. The hand has since healed completely; but the shot remain in it, the doctors being unable to remove them, because unable to determine their exact location. The result is that the hand is almost useless, and often painful.
Hearing of this case, Professor Pupin induced the gentleman to allow him to attempt a photograph of the hand. He used a Crookes tube. The distance from the tube to the plate was only five inches, and the hand lay between. After waiting fifty minutes the plate was examined. Not only did every bone of the hand show with beautiful distinctness, but each one of the forty shot was to be seen almost as plainly as if it lay there on the table; and, most remarkable of all, a number of shot were seen through the bones of the fingers, showing that the bones were transparent to the lead.
In making this picture, Professor Pupin excited his tube by means of a powerful Holtz machine, thus following Dr. Morton in the substitution of statical electricity for the more common induction coil.
Professor Pupin sees no reason why the whole skeleton of the human body should not be shown completely in a photograph as soon as sufficiently powerful bulbs can be obtained. He thinks that it would be possible to make Crookes tubes two feet in diameter instead of a few inches, as at present.
Thomas A. Edison has also been devoting himself, with his usual energy, to experiments with the Röntgen rays, and announces confidently that in the near future he will be able to photograph the human brain, through the heavy bones of the skull, and perhaps even to get a shadow picture showing the human skeleton through the tissues of the body.