Letter: Roentgen Rays Or Streams

Wednesday, August 12, 1896
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August 12, 1896 Roentgen Rays or Streams. To rss: Enrron mr rm: Enscrnxcan Rmvrrwz In theoriginal report of his epochal discoveries, Roentgen expressed his conviction that the phenomena he observed were due to certain novel disturbances in the ether. This opinion deserves to be considered the more as it was probably formed in the first enthusiasm over the revela- tions, when the mind of the discoverer was capable of a much deeper insight into the nature of things. It was known since long ago that certain dark radiations, capable of penetrating opaque bodies, existed, and when the rectilinear propagation, the action on a iiuorescent screen and on a sensitive film was noted, an obvious and unavoidable inference was that the new radiations were transverse vibrations, similar to those known as light. On the other hand, it was dilhcult to resist certain argu- ments iu favor of the less popular theory of material particles, especially as, since the researches of Lennard, it has become very probable that ma< terial streamsgesembling the cathodic, existed in free air. Furthermore, I myself have brought to notice the fact that similar material streams -which were subsequently, upon Roentgen’s announcement, found capable of producing impres- sions on a sensitive film-were ob- tainable in free air, even without the employment of a vacuum bulb, simply by the use of very high poten- tials, suitable for imparting to the molecules of the air or other particles a sufficiently high velocity. In reality, such puiis or jets of particles are formed in the vicinity of every highly charied conductor, the potential of whic is rapidly varying, and I have shown that unless they are prevented, they are fatal to every condenser or high-potential transformer, no matter how thick the insulation. They also render practically valueless any esti- mate of the period of vibration of an electromagnetic system by the usual mode of calculation or measurement in a static condition in all cases in which the potential is very high and the frequency excessive. It is significant that, with these and other facts before him, Roentgen inclined to the conviction that the rays he discovered were longitudinal waves of ether. After along and careful investiga- tion, with apparatus excellently suited for the purpose) capable of producing impressions at great distances, and after examining the results pointed out by other experimenters, I have come to the conclusion which I have already intimated in my former contributions to your esteemed journal, and which I now ind cour- age to pronounce Without hesita- tion, that the original hypothesis of Roentgen will be confirmed in two particulars: Hrst, in regard to the longitudinal character of the disturb- ances; second, in regard to the medium concerned in their propaga- tion. The present expression of my views is made solely for the purpose of preserving a faithful record of what, to my mind, appears to be the true interpretation of these new and important manifestations of energy. Recent observations of some dark radiations from novel sources by Bec- querel and others, and certain deduc- tions of Helmholtz, seemingly appli- cable to the explanation of the peculiarities of the Roentgen rays, have given additional weight to the arguments on behalf of the theory ELECTRICAL REVIEW of transverse vibrations, and accord- ingly this interpretation of the phe- nomena is held in favor. But this view is still of a purely speculative character, being, as it is at present, unsupported by any conclusive experi- ment. Contrarily, there is consider- able experimental evidence that some matter is projected with great velocity from the bulbs, this matter being in all _probability the only cause of the actions discovered by Roentgen. There is but little doubt at present that ei cathodic stream within a bulb is composed of small particles of matter, thrown off with great velocity from the electrode. The velocity probably attained is estiinable, and fully accountable for the mechanical and heating effects produced by the impact against the wall or obstacle within the bulb. It is, furthermore, an accepted view that the projected lumps of matter act as inelastic bodies, similarly to ever so many small lead bullets. It can -be easily shown that the velocity of the stream may be as much as 100 kilometers a second, or even more, at least in bulbs with a single electrode, in which the prac- ticable vacua and potentials are much higher than in the ordinary bulbs with two electrodes. But. now, matter moving with such great velocity must surely penetrate great thicknesses of the obstruction in its path, if the laws of mechanical impact are at all appli- cable to a cathodic stream. I have presently so much familiarized myself with this view that, if I had no exper- imental evidence, I would not question the fact that some matter is projected through the thin wall of a vacuum tube. The exit from the latter is, however, the more likely to occur, as the lumps of matter must be shattered into still much smaller particles by the impact. From my experiments on reflection of the Roentgen rays, be- fore reported, which, with powerful radiations, may be shown to exist under all angles of incidence,it appears that the lumps or molecules are indeed shattered into fragments or constitu- ents so small as to make them lose entirely some physical properties pos- sessed before the impact. Thus, the material composing the electrode, the Wall of the bulb or obstruction of any kind placed within the latter, are of absolutely no consequence, except in so far as the intensity 6f the radia- tions is concerned. It also appears, as I have pointed out, that no further disintegration of the lumps is attend- ant upon a second impact. The mat- ter composing the cathodic stream is, to all evidence, reduced to matter of some primary form, heretofore not known, as such velocities and such violent impacts have probably never been studied or even attained before these extraordinary manifestations were observed. Is it not possible that the very ether vortexes which, according to Lord Kelvin’s ideal theory, compose the lumps, are dis- solved, and that in the Roentgen phe- nomena we may witness a transforma- tion of ordinary matter into ether? It is in this sense that, I think, Roentgen’s Hrst hypothesis will be connrrned. In such case there can be, of course, no question of waves other than the longitudinal assumed by him, only, in my opinion, the frequency must be very small-that of the electro-magnetic vibrating sys- tem-generally not more than afew millions a second. If such process of transformation does take place, it will be difficult, if not impossible, to deter- mine the amount of energy repre- sented iu the radiations, and the state- ment that this amount is very small should be received with some caution. As to the rays exhaustively studied by Lennard, which have proved to be the nucleus of these great realizations, I hold them to be true cathodic streams, projected through the Wall of the tube. _Their deilectibility by a magnet shows to my mind simply that they differ but little from those within the bulb. The lumps of mat- ter are probably large and the velocity small as compared \vith that of the Roentgen rays. They should, how- ever be capable in a minor degree of all the actions of the latter. These actions I consider to be purely mechanical and obtainable by other means. So, for instance, I think that if a gun loaded with mercury were fired through a thin board, the projected mercury vapor would east a shadow of an object upon alilm made especially sensitive to mechanical im- pact, or upon a screen of material capable of -being rende1'ed Huorescent by such impact. The following observations made by myself and others speak more or less for the existence of the streams of matter. ~I-PBENOMENA or EXHAUSTION. On this s11bject'I have expressed myself on another occasion. It is only necessary to once more point out that the effect observed by me should_ not be confounded with that noted by Spottiswoode and Crookes. I explain thelatter phenomenon as follows: The first fluorescence appearing when the current is turned on, is due to some organic matter almost always intro- duced in the bulb in the process of manufacture. A minute layer of such matter on the wall produces invariably this first Huorescence, and the latter never takes place when the bulb has been exhausted under application of a high degree of heat or when the organic matter is otherwise destroyed. Upon the disappearance of the first fluorescence the rarefaction increases slowly, this being a necessary result of particles being projected from the electrode and fastening themselves upon the wall. These particles ab- sorb a large portion of the residual gas. The latter can be again freed by the application of heat to the bulb or otherwise. So much of the effects observed by these investigators. In the instance observed by lnyself,there must be actual expulsion of matter, and for this speak following facts: (a) the exhaustion is quicker when the glass is thin; (b) when the potential is higher; (c) when the discharges are more sudden; (d) when there is no obstruction within the bulb; (e) the exhaustion takes place quickest with an alumi- num or platinum electrode, the former metal giving particles moving with greatest velocity, the latter particles of greatest weight; (f) the glass wall, when softened by the heat, does not collapse, but bulges outwardly; (g) the exhaustion takes place, in some cases, even if a small perceptible hole is pierced through the glass; (h) all causes tending to impart a greater velocity to the particles hasten the process of exhaustion. II-RELATION BETWEEN OPACITY AND DENSITY. The important fact pointed out early by Roentgen and connrrned by subsequent research, namely, that n. body is the more opaque to the rays the denser it is, can not be explained as satisfactorily under any other assumption as that of the rays being streams of matter, in which case such simple relation between opacity and density would necessarily exist. This relation is the more important in its bearing upon the nature of the rays, as it does not at all exist in light- giving vibrations, and should conse- quently not be found to so marked a degree and under all condifions with vibrations, presumably similar to and approximating in frequency the light vibrations. III-DEFINITION or snnnows ON SCREEN OR PLATE. When taking impressions or observ- '79 ing shadows while varying the in- tensity of the radiatious, but main- taining all other conditions as nearly as possible alike, it is found that the employment of more intense radia- tions secures little, if any, advantage, as regards the definition of the de- tails. At first it was thought that all there was needed was to- produce very powerful rays. But the experi- ence was disappointing, for, while I succeeded in producing rays capable of impressing a plate at distances of certainly not less than 30 metres, I obtained but slightly better results. There was one advantage in using such intense rays, and this was that the plate could be further removed from the source, and consequently a better shadow was obtained. But otherwise nothing to speak of was gained. The screen in the dark box would be at times rendered so bright as to allow reading at some distance plainly, but the shadow was not more distinct for all that. In fact, often a gery strong radiation gave a. poorer impression than a weak one, Now, a fact which I have repeatedly ob- served and to which I attach great importance in this connection, is the following : When taking impressions at a small distance with a tube giving very intense rays, no shadow, unless a. scarcely perceptible one, is obtained. Thus, for instance, the flesh and bones of the hand appear equally transparent. Increasing presently gradually the distance, it is found that the bones cast a shadow, while the flesh leaves no impression. The distance still increased, the shadow of the flesh appears, while that of the bones grows deeper, and in this neigh- borhood a place can be found at which the definition of the shadow is clear- est. If the distance is still further continually increased, the detail is lost, and dually only a vague shadow is perceptible, showing apparently the outlines of the hand. This often-noted fact disagrees entirely with any theory of transverse vibrations, but can be easily explained on the assumption of material streams. When the hand is near and the veloc- ity of the stream of particles very great, both bone and flesh are easily penetrated, and the effect due to the difference in the retardation of the particles passing through the hetero- geneous parts can not be observed. The screen can Iluoresce only up to a certain limited intensity, and the film can be affected only to a certain small degree, When the distance is in- creased, or, what is equivalent, when the intensity of the radiation is re- duced, the more resisting bones begin to throw the shadow first. Upon a further increase of the distance the flesh begins likewise to stop enou h of the particles to leave a trace on tie screen. But in all cases, at a certain distance, manifestly that which under the conditions of the experiment gives the greatest difference in the trajecto- ries of the particles within the range perceptible on the screen or film, the clearest shadow is secured. `IV-THE RAYS ARE ALL OF ONE KIND. The preceding explains the appar- ent existence of rays of different kind; that is, of different rates of vibration, as it is asserted. In my opinion, the velocity and possibly the size of the particles both are different, and this fully accounts for the discordant re- sults obtained in regard to the trans- parency of various bodies to these rays. I found, for example, in many cases that aluminum was less trans~ parent than glass, and in some in- stances brass appeared to be very transparent as compared with other metallic bodies. Such observations showed that it was necessary, in mak- ing the comparison, to take rigorously equal thicknesses of the 'bodies and (c