Electro-Physics and Magnetism (Mar. 28, 1896)

Röntgen Rays. SHETTLE. Lond. Elec. Rev. and Elec. Eng. March 6.

—He claims that the cause of the phenomena discovered by Röntgen (referring to the photographic effect of the rays) is the direct result of electric stress and not, as was supposed, of invisible light. He describes an experiment in which a cotton-covered wire “was bent five times upon itself in parallel lines” and then fastened to a cardboard and placed directly on the sensitive surface of a photographic plate; a very thin magnetic strip was fastened to the back of the plate by strips of paper, the whole being wrapped in ruby and in black paper; an alternating current of eight amperes at a frequency of 40 was passed through the wire for about 45 minutes; a complete and distinct image of the magnetic strip and the paper fastening it was formed on the plate. He claims that the “effects were the product of stress in the wire exercised through the glass plate upon the magnet and the paper.” He endeavors to explain the process by which he thinks all photographs are taken; all forms of matter are polar, that is, assume a definite direction, and they are free to move in a magnetic field; owing to the terrestrial magnetism all matter exists in a magnetic atmosphere; when light, which is one of the distributing elements, falls on the sensitive surface, the molecules are thrown into motion and the general effects on the surface are the same; when it is reflected from an image the counterpart of that image would be produced on the plate; he claims that the same principle holds good in images obtained by the stress of magnetism, as the sensitive matter on the plate registers the various directions in which impressions have been conveyed to it directly or indirectly, through intermediate bodies; any body which intercepts the lines of stress modifies their effects on the plate; bodies of greater density interfere more with the lines of stress. Editorially it is thought that the image obtained by Dr. Shettle is due to electromagnetic induction and has nothing to do with the magnetic field produced by the magnet, a bar of soft iron it is thought would act equally well (from the photograph there appears to be no difference whatsoever between the poles and the middle of the magnet; also that where the paper overlaps the magnet the image is darker; the image of the magnet and the paper are about equally dark); the alternating current through the gridiron conductor would induce currents in the gelatine filament and this would cause decomposition of the salts in proportion to their intensity; the presence of the metallic bar on the back of the plate would modify the intensity of the currents in the film immediately above it (but the paper, which is a non-conductor, appears to act like the magnet, as far as causing the image is concerned).

Another article in the Lond. Elec. Rev. gives a brief summary of recent developments. The doubt which was expressed as to Blythswood’s experiment being a genuine photographic effect has been removed by further experiment; at the suggestion of Lord Kelvin the sensitive plate was placed in a tight zinc box with an aluminum window in the lid, the box being carefully earthed and placed between the two poles of the large influence machine, which latter were two feet apart and produced a silent brush discharge; the object was placed either inside the box or outside on the aluminum window; photographs were obtained in half an hour. It is thought that the long-known electric shadows produced by influence machines may be due to the same cause; Holtz produced these shadows by using a point and a disc on his machine, the disc being hollow and covered with silk; conducting bodies between the point and the disc threw distant shadows on the silk of the disc, while insulating bodies were apparently transparent; he therefore concluded that the nature of the surface was important in determining the transparency; Lehmann found by using a disc on each electrode that a shadow of the interposed body was projected on the faces of both discs. Gossart and Chevallier made a curious discovery (see Comptes Rendus, 122, p. 316) which appears to add to the mystery concerning the nature of the radiations in the Crookes tube; they found that the Röntgen rays exercise a mechanical directive action on the vanes of the wheel in the Crookes radiometer; they created a field of force inside the radiometer, which is opposed to that due to the heat; the direction and intensity of the field of force around the Crookes tube was explored by means of the radiometer; it was found by experimenting with 20 substances that this force was transmitted and arrested by the same media as the Röntgen rays are; only when the radiometer was placed in the Crookes field was the field “modified by currents, especially by those of the exciting coil of the Crookes tube, modified by the presence of statically charged electrified bodies; and finally energetically distributed by a magnet”; by moving a magnet circularly about a radiometer the vanes in some way are set free and become again obedient to a source of heat; when placed in the path of cathode radiations the motion of the vanes is dampened, sometimes one pair and sometimes another taking up the axial position of equilibrium; when the current in the Crookes tube ceases the directive action of the vanes persists for about five minutes afterward in spite of the constant action during that time of the Locatelli lamp; the vanes may be started again by directing on them the radiation from the anode, when they will at first undergo an impulsion opposite to the normal direction, which they afterward resume; the inertia effect, which lasts for five minutes, was obtained with a Ruhmkorff coil, but a Wimshurst machine failed to produce it; paraffin was found to be more transparent than air.

Henry thinks that his experiments verify the hypothesis of Poincaré that all fluorescing bodies emit Röntgen rays; a faint white image of a wire placed between a fluorescing body which had been exposed to light and a sensitive plate was produced on a dark rectangular background. Meslans made experiments to determine the influence of chemical constitution in the transparency of bodies to the Röntgen rays (see Comptes Rendus, 122, p. 309); he found that carbon and its compounds with hydrogen, oxygen and nitrogen is extremely transparent, but when combined with chlorine, sulphur, phosphorus or iodine, its opacity is considerably increased; he believes that the difference in the chemical constitution of the materials forming the nerves and the blood will without doubt enable photographs of these constituents of the body to be obtained by virtue of their unequal transparency. Prof. J. J. Thomson, in Nature, gives an account of some very interesting investigations; he tried to determine the leakage in air at different pressures; in following up his discovery that all bodies become conductors when traversed by these rays, he found that the rate of leakage is greater at a high pressure than at a low one, and for a wide range is approximately proportional to the square root of the pressure; he believes the leakage of electricity through non-conductors is considered to be due to a kind of electrolysis, “the molecule of the non-conductor being split up by Röntgen rays, which act the part played by the solvent in ordinary electrolytic solutions”; he obtained indications that the rate of leakage through air is proportional to the number of ions; he concludes that the Röntgen rays are not all of the same kind, and that their penetrative power varies greatly with the efficiency of the tube which produces them; he found that most tubes improve for a time after they are sealed off, and after attaining a maximum efficiency they then deteriorate.

According to the Jour. des Inventeurs, March 1, Mr. DE HEEN wrote to the French Academy of Sciences that according to his experiments the Röntgen rays of Lenard and Röntgen did not emanate from the cathode, but from the anode; to demonstrate this, one has only to place between the Crookes tube and the sensitive plate a screen of lead perforated with several holes allowing the rays to pass through; the direction of these on the photographic plate indicate that they emanate from the positive and not from the negative pole and that they are therefore anode rays.

According to the Elek. Zeit., March 5, SATORI in Vienna stated that he obtained very intense Röntgen rays with a comparatively small influence machine by connecting the Crookes tube in series with a spark gap and in parallel with two condensers “whose outer coatings were short circuited,” the machine gave a spark of about 12 cm; the result was not successful when the spark gap, which is in series with the tube, was omitted, probably because the voltage was then too low; that this method is much cheaper and simpler than the one usually used is self-evident, besides requiring no source of current, as the machine is turned by hand.

The paper by Mr. Perrin, noticed in the Digest, March 14, is published in full in the Bul. Soc. Int. des Elec. for February.

Present Ideas Concerning Cathode Rays. GUILLAUME. La Nature, Feb. 29.—He considers that the phenomena discovered by Röntgen is already becoming less mysterious and there appears a possibility of explaining it without having recourse to any new ideas; he believes that Raveau has come nearest to a satisfactory theory based on a remark of Prof. Schuster. In a previous article in that journal (July 28, 1894) Guillaume reproduced two photographs obtained by Lenard showing two spots produced by the cathode rays which are deflected and which are not deflected by a magnet; they show that the original rays consist of two distinct kinds, one of which is nearly independent of the effect of the magnet, while the other was deflected by a magnetic field into a band like a spectrum. He thinks it an established fact that the Röntgen rays are derived from the cathode rays, but are not cathode rays themselves; there is a great probability that the Lenard photographs were produced by two kinds of rays, one the true cathode rays and the others which are not deflected. There are at present two hypotheses, that of bombardment and that of radiation; that they are contradictory is not surprising if it is true that heretofore two absolutely different phenomena have been observed together. There is no doubt that Röntgen rays are essentially different from the cathode, and that they are produced at the point of impact of the original ones on a body; they diminish as the square of the distance measured from the point of impact. If the rays proceed in straight lines from the point where they are produced, it is none the less true that they do not come in a straight line from the cathode to objects exterior to the tube. He considers that the tests of the theory of longitudinal vibrations of the ether have not met with success, and he thinks this theory ought to be rejected, adding that it might be kept in reserve for the future “to be given in a still more embarrassing case.” Lenard thought his phenomena might be explained by the hypothesis of very short wave-lengths; the difficulties in the way appear great, but he thinks Raveau has overcome most of them; it is known that ultra-violet radiation, which in general is very refrangible, is capable of traversing a body without being deflected or strongly absorbed; the abnormal refraction discovered by Lerous was considered an exceptional phenomenon; it consists in a reversing in the order of refrangibilities. Kundt found that many metals have an index less than unity in the visible spectrum and it is therefore natural that they possess a strong absorption and that when the band has once been passed they become more transparent; the coefficient becomes less than unity at the extremity of the band and increases again asymptotically toward unity; if it has been thought that most bodies are completely absorbent for low wave-lengths, it was perhaps due to the fact that it was not possible to produce sufficiently short waves; Chardonnet long ago showed the transparency of silver to ultra-violet rays.

Longitudinal Light. JAUMANN. Lond. Elec., March 6; the first part of a translation of a paper from the Wied. Ann., 51, p. 147.—The style is somewhat brief and not very clear. He gives results of experiments concerning the nature of light in a vacuum and of cathode rays, accompanied by a theory of electric phenomena in rarefied air, which he considers makes cathode rays and kindred phenomena perfectly intelligible. The first part refers to the determination of the direction of vibration of electric rays, which direction he states may be determined by discharge experiments; he gives what he calls a discharge law and shows how it can be used for determining the direction of vibration of cathode rays and of light in rarefied air; he claims to have given an experimental proof of the longitudinal character of cathode rays founded on the discharge effect of these rays; as they have a strong discharge effect he claims they are electric waves of great amplitude; they also have a strong discharge effect when their direction is perpendicular to the electrode surface and hence the direction of their electric oscillation coincides with their direction of propagation; “they are rays with a great longitudinal component, and, therefore, from symmetry, essentially pure longitudinal electric rays.”

Movable Light Phenomena in Rarefied Gases Caused by Electric Oscillations. ELSTER and GEITEL; Elek. Zeit., March 5; abstracted from the Wied. Ann., 56, p. 733.—They describe experiments from which they conclude that cathode rays are not due to a bombardment of particles detached from the electrode, but are movements of the ether analogous to light, that is, to what Jaumann calls longitudinal light.

Resistance to Alternating Currents. BRYLINSKI. Bul. Soc. Int. des Elec., February.—A communication referring to the recent paper of Mascart (Digest, Feb. 8 and Jan. 18). He gives a formula for finding the increase in the (apparent) resistance (due to the frequency) of copper wires of any given diameter for a frequency of 80; after reducing the formula of Mascart to the same form, he compares numerical results obtained from both of them for various diameters, with the results in the table of Lord Kelvin, showing that his (Brylinski’s) formula gives closer results, although the other is sufficient for practical purposes. He then discusses the subject of iron wires, coming to conclusions which are quite opposite to those arrived at by Mascart; he finds that the increase of resistance produced by high-frequency currents in iron wire appears to be the only reason why it is impossible to use iron for long-distance telephone lines, while Mascart concluded that iron wire was better, all other conditions being the same; he takes a numerical example assuming the permeability to be about 100, according to Massin, and finds that the increase of resistance is much greater than for copper; in a table he gives the effective resistances of various iron wires for the frequencies corresponding to certain sounds of the human voices.

Experiment with an Incandescent Lamp and Magnet. SALOMONS. Lond. Elec. and Elec. Eng., March 6; a brief abstract of a Physical Society paper.—When an incandescent lamp through which an alternating current passed, was brought near a continuous-current magnet the filament was found to be set into vibration; if brought sufficiently near, the vibrations were sufficiently intense to break the filament; the number and position of the nodes formed were found to be independent of the natural period of the filament, but depend on the frequency of the alternating current. Prof. Ayrton suggested that the magnetic leakage was very large in that experiment and wanted to know whether this method was more sensitive for mapping out the field than those ordinarily employed; he thought that the natural period of the filament would to a certain extent influence the results; he called attention to some measuring instruments in which a similar principle was made use of. Salomons replied that the arrangement was not intended for making measurements; the character of the vibrations remained unaltered for many hours; he found the vibrating filament useful for microscopic work, where a surface rather than a line of light was required.

Röntgen Rays.—The Elec. Rev., March 11, contains an interesting article by Mr. TESLA, giving his views and results obtained by him, including a large reproduction of a photograph of the shoulder of a man, showing the ribs and upper arm bones taken at a distance of 4 feet, and another showing a clear image of wire taken at a distance of 11 feet. His experiments were directed toward investigating the nature of the radiations and to perfecting means for their production; their intensity depends on the intensity of the cathode streams, and he concludes that the highest obtainable electric pressure is therefore desirable; the best results would therefore be obtained by using the disruptive discharge with which there is practically no limit to the spark-length, the only requirement being a certain knowledge and skill in the adjustment of the circuits, particularly as to resonance. By having two electrodes in the same bulb the potential is limited and one is therefore led to the use of a single electrode bulb, the other terminal being as far away as possible; an inside terminal should be used as tubes without such terminals are much less efficient on account of loss through the glass; it is an error to suppose that concave electrodes will concentrate the rays; they are if anything a disadvantage. Regarding the vacuum, he calls special attention to an electrical method of rarefaction which may be used to any degree desirable, and gives a vacuum far beyond that obtainable by any mechanical appliances; although this can be done by means of a static machine, a disruptive coil is far better; after exhaustion with an ordinary vacuum pump, the bulb is attached to the disruptive coil, and there will then be at first a milky light throughout the bulb, and the phosphorescence of the glass, which subsides quickly, and a white light then settles around the electrode, a dark space forming at some distance from it; the light then becomes reddish and the terminal grows very hot, requiring careful regulation to prevent it from being consumed; after this the light again becomes white and gets weaker and weaker until the streams finally disappear, the phosphorescence growing more intense and the spot where the stream strikes the wall becomes very hot, the phosphorescence around the electrode ceases and it becomes quite cool; the gas in the tube has then reached the required degree of rarefaction; the process may be hastened by repeated heating and cooling and by the use of a small electrode; bulbs with external electrode may be treated in the same way; whenever the electrode is as hot if not hotter than the glass, it is a sure indication that the vacuum is not high enough or that the electrode is too small; as a cooling medium he found it best to use jets of cold air, thus enabling one to use very thin tubes. He thinks the opacity of the glass and transparency of aluminum have both been somewhat exaggerated. He believes that there is an actual expulsion of the particles through the walls of the bulb; he is becoming more and more convinced that the phenomena is due to a stream of material particles which strike the sensitive plate with a great velocity; based on an estimate of Lord Kelvin, he believes that with very high potentials the speeds are as great as 100 kilometers a second. Even an ordinary stream under a great pressure passes through a thick glass plate as though it were not there; from a low to the highest frequency obtainable there seems to be no difference in the quality of the effects produced except that they are more intense when the frequency is higher, which he thinks is due to the fact that the maximum pressures of the cathode are then also higher; this is on the assumption that the effects on the sensitive plate are due to projected particles or else vibrations far beyond any frequency which can be obtained by means of the condenser discharges; the fact that the opacity of a body bears some relation to the density speaks strongly for the material streams; strong impressions on the plate might be arrived at by perfecting plates especially sensitive to mechanical shock or impact; this may lead to the abandonment of the present plate. He has obtained remarkable impressions with the apparatus described; shadows may be obtained at distances of many feet while at small distances and with thin objects an exposure of a few seconds is sufficient; he hopes to be able to magnify the effects many times; with a rabbit exposed for one hour, not only the skeleton was visible, but there was also a clear outline of the abdominal cavity, the location of the lungs, the fur and other features being also shown; images of human limbs are obtained in a quarter of an hour to an hour; metallic objects and bony or chalky deposits can now be invariably detected in any part of the body; an outline of the skull is obtained in 20 to 40 minutes, the latter showing the cavities of the eye, and the chin, cheek and nasal bones, etc., as also the flesh and even the hair; the action of the rays on the head appears to cause a feeling of drowsiness, a sensation of warmth and a general soothing effect. It may be possible, he thinks, by these strange appliances to project a suitable chemical into any part of the body. The issue of March 18 contains a further contribution from the same author. After making a few corrections in his former article, he states that he is now producing strong shadows at a distance of 40 feet and even more, with “the possibility not to say certitude of augmenting the effects with my apparatus at least ten-fold”; he attributes the effects of this great distance to the use of a bulb with a single terminal which permits the use of practically any desired potential and the attainment of extraordinary speeds of the projected particles. He also obtained shadows by reflected rays only, thus demonstrating that the rays possessed this property; a thick copper tube was used at the one end of which the plate holder was placed, while at the other, open end, there was a thick plate of glass at an angle of 45 degrees above which was the bulb; a clear, sharp shadow was produced with an exposure of 45 minutes; he satisfied himself that no action would be produced through the copper tube; he also found that approximately 2 per cent. of the rays were reflected. He is finding more evidence in support of the theory of moving material particles and is arranging some crucial tests; a fairly exhausted bulb containing the electrode connected to the disruptive coil produced small streamers breaking through the sides of the glass, producing a fine hole through which, however, the air does not rush into the tube; the glass in the neighborhood of the rupture may grow hot enough to soften but it will not collapse but rather bulge out, showing that the pressure from the inside is greater than that of the atmosphere; as the matter is expelled from the bulb the rarefaction increases and the streamers become less intense, whereupon the glass closes again, hermetically sealing the opening; he thinks this a positive evidence that matter is being expelled through the walls of the glass.

The same journal contains brief extracts from articles published in daily papers, among which is one stating that Edison found that he could see with the naked eye all the bones of the hand, also moving objects through eight inches of wood; he states that it makes a great difference who does the glass blowing for the bulbs, as the nature of the breath of the glass blower is said to make a difference.

The West. Elec., March 21, contains an article by Mr. JONES in which he expresses the belief that there is an analogy between ordinary light and this new radiation; the latter seems to be made up of many different rays which differ widely in penetrating power, just as white light is the sum of rays of various wave-lengths; the time of exposure decreases with the rise in voltage, but lower voltages will also produce radiations; a sheet of aluminum is fairly opaque to low potential radiation but quite transparent to those produced by higher voltages; he thinks his experiments justify the theory that Röntgen rays vary greatly in penetrating power and that the voltage at the tubes plays a similar part to temperature in producing light rays, new waves being excited as the temperature rises; he is carrying out further experiments. His results also indicate that each ray requires a definite time to produce its maximum effect; an experiment is described showing that particular rays produced their maximum effect in 5 to 15 minutes and that a longer exposure was useless.

E. P. THOMPSON, in the Elec. Eng. and West. Elec., March 7, describes an application of the X-rays for seeing objects in motion; with the apparatus referred to in the Digest, Feb. 29, he saw the motion of the bones of the fingers when bent backward and forward; he believes that with this apparatus the skeleton of a fish could be seen in the act of swimming; he thinks a fracture in a limb could thus be made visible by bending or stretching the limb; another experiment showed the effect of a solid passing through a solid, which suggests a possibility in surgery where it is desirable to follow the point of the instrument through the flesh. He finds that certain precautions are necessary in preparing the fluorescent screens; when the barium platino-cyanide is crystallized on a sheet of paper, or if the crystals are pressed on the surface, the screens are of little use; excellent results were obtained when the cyanide was powdered as finely as possible and applied with the clearest colorless varnish on a piece of tracing cloth, to the depth of about one eighth of an inch, care being taken not to make it too thin; either side of the screen may be directed toward the tube; it is important to perform the experiments in a dark room.

The Elec. Eng., March 11, contains an article by Prof. STINE in which he covers partly the same ground as in the article abstracted above. He considers that his experiments strongly confirm the theory of longitudinal vibrations; he has not been able to detect that the light speed of dry plates has an influence on the time of exposure to the X-rays, and he now prefers slow plates, as they give clearer shadows; an experiment seems to indicate that ultra-violet rays have nothing to do directly with the phenomena; he appears to think that fluorescence is not the cause of the photographing action; the anode and cathode streams seem to be identical; he tested many incandescent lamps as bulbs for producing these rays, and found only one that would answer, from which he concludes that the vacuum is too low; he obtained some negatives of tourmaline, which he thinks proves that the rays are not transverse in character, and that the ultra-violet wave theory can no longer be entertained. He calls attention to the difference between such photographs and the so-called “electrographs,” which latter he thinks are the result of an electrolytic action on the silver salts; he considers that the cathode is the prime source, but that the fluorescent bulb is a secondary source; the yellowish-green fluorescence is thought to be due to the uranium in the glass; he made other experiments with uranium to find whether it was the cause of the rays, and did not obtain the slightest effect; the Crookes tubes should have an extremely high vacuum, so high that there is only a faint trace of purple light around the anode; a successful tube shows a green fluorescence, while in those that failed it is yellow; a tube improves with use; he thinks the photograph is not the result alone of molecular bombardment, but rather of the nature of electrolysis; the seat of the effect may be in the molecules containing a charge of static electricity and vibrating with a frequency of green fluorescence or ultra-violet light.