Röntgen Rays

The Elec. Rev., April 1, contains another communication from Mr. Tesla, the greater part of which is descriptive of his researches with the reflection of Röntgen rays, including an illustration of the apparatus used. His researches have strengthened his conviction that the rays are streams of material particles possessing a great velocity, and they should therefore be capable of being reflected; he describes and shows a form of tube which consists of a cylinder of very thick glass, the bottom of which is made very thin, and the top of which contains the single electrode which should be of aluminum, as platinum gives inferior results, and the bulb is disabled in a comparatively short time; he describes briefly how a fairly constant vacuum may be maintained and produced electrically. It is not literally true that the Crookes vacuum is not high enough for producing the Röntgen phenomena, which manifest themselves even with poor vacua, provided the potential is high enough; to prevent overheating when the potential is raised, the number of impulses or their duration should be reduced, and it is therefore well to use a rotating commutator in connection with the ordinary coil instead of a vibrating make-and-break; with this rotating commutator the conditions may be adjusted to suit the degree of the vacuum and the potential. In his experiments in reflection he used a T-shaped box of lead, which was found to be entirely impervious; the bulb was placed at one end of the straight piece, and the sensitive plates were placed over both of the other ends, the reflecting plate being secured at the proper angle in the middle; one plate would therefore be affected by transmitted rays and the other by those which are reflected; images which were exactly alike were placed over the two plates. The results of the observations are given in a table for 12 different materials most of which were metals, and approximate calculations were made to show the relative impression by reflected rays, which appears to have varied from o per cent. for aluminum to 3 per cent. for zinc, the percentage being based on the impression by direct action; he considers these figures fairly correct as relative values; arranging the metals according to these values, he arrives at the following order: zinc, lead, tin, copper, silver; this order is precisely that in the contact-series of metals in air, which if true he considers an extraordinary fact; the one possible explanation he thinks is that the bulb throws out streams of matter in some primary condition and that their reflection depends on some fundamental and electrical properties of the metals; this seems to infer that these streams must be of uniform electrification, that is, anodic or cathodic, but not both. He does not agree with the statement that the streams are anodic, as he finds that both affect the plate; also that the phosphorescence of the glasses has nothing to do with the photographic impressions, for when aluminum vessels are used there is no phosphorescence. In connection with induction coils, both terminals of a tube are acted upon alike, as long as the tube is not very highly exhausted; at a high degree of exhaustion both electrodes act practically independently and the coil is then unbalanced; a hot anode emits a more intense stream than a cool cathode. He found that a brass plate of 1/8 inch thickness proved fairly transparent while copper and zinc plates of the same thickness were entirely opaque. With the use of proper reflectors he produced stronger effects; by surrounding a bulb with a thick glass tube the effect may be considerably increased; the use of a zinc reflector showed an increase of about 40 per cent.; by the proper use of reflectors any number of bulbs may be used, thus producing any desired intensity of radiation. He has failed so far in his efforts to demonstrate refraction, although he tried a great many experiments. The issue of April 8 contains another communication from him. In making further experiments with reflection he used two metallic plates simultaneously, placed next to each other, so as to compare their reflecting power; a thick lead plate divided the box into two halves to prevent the rays from intermingling; the result showed that iron reflected about as much as copper, and that tin was a trifle better than lead, also that magnesium was a little better than zinc. He found it possible to reduce the time of exposure of plates to a few minutes with the aid of fluorescent paper placed near the sensitive film. Although zinc reflected only 3 per cent. of the rays when the angle was 45 degrees, the amount would be much greater for larger angles, and as such a large proportion of the rays radiate out into space, a reflection of even a small proportion of them may increase the effect several times; as an evidence of the effectiveness of such a reflector, he shows a print of the shoulders and ribs of a man which was obtained with the aid of a funnel-shaped reflector in connection with the tube; the exposure was 40 minutes, and the plate showed very strongly every bone and rib; the chief use of the reflector is that it allows the use of many bulbs without sacrifice of precision, as also a concentration on a small area. By the use of fluorescent bodies in connection with a sensitive film, he has shortened the time of exposure to even a few seconds; owing to the large size of the crystals of tungstate of calcium, the impression is not very clear; for use in connection with sensitive films it should therefore be ground very fine and distributed uniformly and the paper should adhere firmly to the film all over the plate. The fluorescence of this body seems to depend on a peculiar radiation, as it was different with different bulbs, which otherwise worked very successfully; an impression of a hand was taken at six feet in less than a minute, and even then it was over-exposed; the bulbs are very apt to explode, owing to the great internal pressure against the bombarded spot; when using phosphorescent paper in connection with the film the time of exposure is reduced so much that the thickness of the object is not of very much consequence. The fluoroscope of Edison, he states, is really Salvioni's cryptoscope with the lens omitted, which he thinks is a great disadvantage; with it he could easily distinguish the spinal column in the upper part of the body, which is more transparent than the lower, at a distance of about three feet from the bulb; through the body he could easily see the shadow of a square plate of copper; he thinks that improving the fluorescence will not add much in the examination of the internal parts of the body, and that the solution will probably come through the production of very powerful radiations; the fluoroscope does not give nearly as clear impressions as the photograph; the use of the screen for noting the effects of reflection, refraction and diffraction proved futile. The same journal publishes some comments on Tesla's work, by others, which, however, contain nothing of importance, technically.

The same journal contains an interview with Prof. Salvioni. He mentions briefly that he endeavored to find the velocity of the rays, so as to decide whether they are light or matter, and the conclusions so far obtained lead him to believe that they are matter, but he is not sure of the result; he also attempted to find whether objects present color phenomena analogous to those of light, and the results so far have been negative, giving support to the supposition that the rays are projected matter, but he has not yet reached definite conclusions. In the impression of a frog, if over-exposed, the ribs disappeared, showing the lungs, heart and another organ corresponding to the spleen. He also studied the transparency of the eye, arriving at the conclusion that it is hardly transparent. He describes his cryptoscope (see Digest, March 14). In an experiment he noticed that when he touched the tube with the hand, the luminous aspect varied, the tube first losing its fluorescence, which is then re-excited, reaching a great maximum, and is then relegated to the anode; it is sufficient to bring a metallic point connected with the earth or with the cathode, in contact with the tube, to obtain a very intense fluorescence confined to about one square centimetre, opposite to the place at which the tube is touched; “with this system the exhaustion of the tube can also be avoided, as with the metallic point the fluorescent zone can be successively displaced.”

McClure's Magazine contains an interview with Prof. Röntgen by a reporter of that journal, which is reprinted in the Elec. Rev., April 1; parts of it are interesting, although it does not contain anything of importance scientifically.

The Elec. Eng., April 8, contains a short article by Mr. Edison suggesting that the X-ray was a sound wave of very small wave length, and that the shadows were sound shadows; he refers to an article by LeConte in the Phil. Mag., Feb., 1882, a reprint of which with illustrations accompanies the article, on experiments with sound shadows. Edison describes an experiment in which the source of X-rays was placed on one side of a steel plate and on the other side it was noticed by means of the fluoroscope, that the rays seem to be refracted or bent around the edges of the plate. In another experiment which he believes tends to confirm the theory, he found that liquids do not fluoresce, while crystals alone do, crystal being “resonant to the wave.” In another experiment he found that a tube with too low a vacuum, which ordinarily produces no X-rays, can be made to generate them by a powerful blast of air on the spark of the break wheel, and a spark gap in the secondary. Another observation was that the sharpness of the shadow depends on the abruptness of the break. With Sprengel pumps used for incandescent lamps, the vacuum is too high for the best results; if a definite amount of air is allowed to enter the bulb, the rays will flash out with great brilliancy, diminishing again as the exhaustion is continued.

The same journal contains an article by Dr. Morton, in which he gives an illustrated description of a bulb with a piece of fluorescent material mounted in it, and from this he believes the X-rays proceed. He also describes another form of tube, consisting of a glass cylinder, with rounded ends, having an external electrode in the form of a disc of aluminum at one end, and a cap of aluminum covering the other end and the greater part of the walls of the tube, the edges nearest the other electrode being serrated, to provide for possible sparking between the electrodes and thus prevent perforation of the tube; the rays pass through the large cap-shaped anode, the cathode being the smaller one; this bulb is said to work well with a static machine.

The same journal contains an article by E. P. Thompson, describing experiments to determine whether ordinary phosphorescence will produce these rays; while his experiments do not prove that the rays do not have their source alone in the phosphorescence of a charged tube, yet he believes that they form substantial evidence that the rays are not obtained from phosphorescence by sunlight. There is also published in the same issue a reprint of a Röntgen photograph of 29 different objects, made by Prof. Terry, of the U. S. Naval Academy.

According to the Amer. Jour. of Science for April, DOELTER showed that different gems may be distinguished from each other and from their imitations by means of the X-rays; the true diamond may be distinguished from the false one; rock crystal, topaz, strass and spinel are opaque to the rays, while the varieties of the corundum, such as the ruby and sapphire, transmit them to some extent; among the minerals there are exceptions to the accepted relation between the opacity and the density; sulphur, realgar, quartz and fluorite are quite opaque; corundum transmits somewhat, while diamond and graphite transmit much better; silicates are opaque, which is also true of mica in layers of one mm; in sections of about one third mm it is possible to distinguish between the transmissive powers of amphibole, garnet, quartz, mica and feldspar.

The Sc. Amer., April 4, contains a brief description of some of Edison's experiments.

Electricity as an Exact Science. CROCKER. Elec. Eng., April 1. — A brief report of a recent lecture before the Franklin Institute. He showed that electricity was one of the exact of the known sciences, being second only to astronomy; the most important test of the science is the power of prediction; a dynamo or motor can to-day be calculated from drawings before the machine is built, more nearly than by a test made of the machine itself; this assertion cannot be made of a steam engine or other like machines; other illustrations of the exactness of the science are given.