April 30, 1896] 



NATURE 



lemonstration of the existence of a regular reflection. Mr. 

 I'esla infers regular reflection from his theory of bombardment. 

 I lis experimental method is the same as that of Prof Rood ; 

 that is, he places a reflecting plate at an angle of forty-five 

 degrees to the direct ray, and then places the photographic plate 

 at right angles to the direction in which the reflected ray should 

 ]3ass if regular reflection existed. On account of the greater 

 power of his apparatus, his time of exposure was one hour, 

 whereas that of Prof. Rood was ten hours. It is evident, how- 

 ever, that an effect upon the photographic plate does not prove 

 the existence of regular reflection." 



In his own experiments on reflection, Prof. Pupin aimed at 

 getting rid of the photographic plate and substituting the fluor- 

 escent screen in its place. 



He concludes as follows : — " These experiments prove beyond 

 ill reasonable doubt that the Rontgen radiance is diffiusely scat- 

 tered through bodies, gases not excepted. We may call it diffuse 

 reflection, if we choose, provided that we do not imply, thereby, 

 that we must necessarily assume an internal inter-molecular 

 regular reflection, in order to explain the phenomenon. For if 

 a puff of smoke be forced through a pile of wood, some of it 

 will come out pretty well scattered, although we cannot speak 

 here of a reflection in the ordinary sense, but rather of deflec- 

 tion, reserving the term ' reflection ' for those particular cases in 

 which the angle of incidence is equal to the angle of deflection. 

 It might turn out, for instance, that the X-rays are due to a 

 circulating motion of ether, and that the stream lines are 

 ileflected and diffusely scattered within the molecular interstices 

 of ponderable substances. Appearances seem to speak more 

 in favour of this view than in favour of a wave motion 

 of ether. The diffuse scattering of the Rontgen radiance 

 by bodies placed in its path may be also described by 

 saying that ez'ery substance when subjected to the action 

 of the X-rays becomes a ractidtor of these rays. . . . The fact 

 that opaque bodies, like metals, are less effective in produc- 

 ing this secondary radiation, leads to the conclusion that there 

 is in these bodies,an internal dissipation of the Rontgen radiance 

 much greater than in the case of transparent dielectric sub- 

 stances. A properly constructed bolometer should give us much 

 information on this point, and it is my intention to take up this 

 -ubject as soon as time and facilities will permit. These diffu- 

 -^ion effects, which are present even in air, bring the Rontgen 

 radiance into still closer resemblance to the principal features of 

 the kathode rays which were studied by Prof. Lenard. The 

 difference in their behaviour towards magnetic force is still to be 

 explained. Is it not possible that this magnetic effect in air is 

 masked by the diffuse scattering of the X-rays ? " 



Our American correspondent says: — " Tesla has found that 

 the X-rays are reflected from certain metals tested in the same 

 order as in Volta's electric contact series in air. Zinc reflects 

 3 per cent, at an angle of 45°. Below it stand lead and tin, hut his 

 observations do not yet show which reflects more highly. Below 

 these in order come copper and iron about the same, then silver. 

 His first observations led him to infer that magnesium would 

 reflect still more than zinc, and sodium most of all. Subse- 

 quent experiment has verified the conjecture as to magnesium ; 

 but sodium has not yet been tested. By availing himself 

 of the reflection from a zinc cone, he has taken a picture 

 of the ribs of an assistant at a distance of four feet from the 

 vacuum tube, and with an exposure of forty minutes. His ap- 

 paratus is so constructed that the bulb or bulbs are at the large 

 end of the cone, and the subject at the small end, where the rays 

 are concentrated. The cone or funnel is constructed at an angle 

 less than 30", so that the incident rays are reflected more than 

 3 per cent ; and especially more the small end of the funnel 

 the rays approach within a very few degrees of parallelism with 

 the reflecting zinc. Prof. Tesla thinks the theory that the X-rays 

 consist of streams of radiant matter, is confirmed by these 

 results. He has not yet been able to detect any refraction of the 

 X-rays." 



In the summary of work done in connection with Rontgen 

 rays (page 522), we give an account of experiments made by 

 Prof. Joly, which demonstrate the existence of reflection. 



" In .confirmation of these experiments," writes Mr. Alfred W. 

 Porter, " may I point out that a similar phenomenon to that 

 flescribed by Prof. Joly has been present on all my skeletal 

 radiographs. Immediately surrounding the sharp geometric 

 hadow of the flesh of the fingers a black line exists on the 

 ■icgativc. This is especially noticeable where two fingers overlap 

 >ne another ; the partial shadow cast by one finger preventing the 



NO. 1383. VOL. 53] 



deposit on ihe plate from becoming so dense as to obscure h 

 presence of the black line. I enclose a positive which shows the 

 presence of the corresponding white line very clearly. My 

 attention was first called to the presence of this line on my 

 pictures on January 28, by Mr. John T. Morris, of this College. I 

 believe that the prominence of the finger-nails is due to the same 

 cause. I have also taken graphs of over-lapping wood, metal, 

 .and ivory objects which exhibit the same phenomena. " 



We have received the prints referred to by Mr. Porter, and 

 they entirely bear out his description of the appearance 

 presented. 



For some time past Prof. FitzGerald and Mr. Fred. T. 

 Trouton, at Trinity College, Dublin, have sought evidence of 

 crystalline action, both on transmission and reflection at grazing 

 incidence of Rontgen rays. Though so far this has been with- 

 out success, we learn that they have noticed a marked scattering 

 of the rays in transmission through some substances. The follow- 

 ing arrangement is convenient for showing this. " On a plate 

 of lead, which has a slit cut in it, is placed a sheet of, say, solid 

 paraffin 2 or 3 m.m. thick, so as to cover one end of the slit ; over 

 this is laid a strip of lead — but slightly wider than the slit — so as 

 to just entirely cover the slit. No direct radiation then can pass 

 from k Crookes' tube, placed vertically over the slit, to a sensitive 

 plate placed behind the lead ; but with a lengthened exposure 

 (20 to 30 minutes) with a focus tube, a darkening is found on 

 developing at the end where the paraffin is placed. If the 

 paraffin be then moved to the centre or other end, so as to 

 eliminate accidental effects, on again exposing the darkening 

 action is found to follow the paraffin. Some darkening always 

 occurs even where there is no solid body. How much of this is 

 due to successive reflections from the lead sheet and strip, or 

 how much is due to scattering of the rays by air, is not easy 

 to say." 



Mr. Dayton C. Miller has obtained some good results at 

 Case School of Applied Science in Cleveland, Ohio, U.S.A., 

 but the exposures he finds necessary are longer than those given by 

 the foremost workers in Great Britain. The tube used by him is 

 spherical in shape, and about five inches in diameter. The coil 

 gives a six-inch spark in air, and is excited by a current of about 

 sixty watts, obtained from fifteen cells of storage battery. The 

 voltage used varies from twelve to twenty. With this apparatus 

 and power, Mr. Miller says : — 



" The bones of the fingers are distinctly shown with exposures 

 of ten seconds, while exposures varying from two to ten minutes 

 are regularly used in locating bullets and shot in the hand, and 

 in examining injured or deformed hands. An excellent picture 

 of a hand and fore-arm, placed diagonally across an 11 x 14 

 plate, has been made with twenty minutes' exposure. The 

 entire detail of the lettering and design of an aluminium 

 medal has been taken in five minutes. Numerous interesting 

 surgical cases of fractured and diseased arm-bones have been 

 examined with satisfactory results. Photographs of the chest 

 and head have been made with exposures of one hour in each 

 case. A surprising amount of detail is visible. The chest 

 picture shows the shoulder-joint, the collar-bone, the spinal 

 column with its articulations, and a dark streak along its length 

 corresponding to the spinal cord, and eight ribs on each side of 

 the spine. In the region of the heart the detail is less con- 

 spicuous, indicating that the heart is more opaque than the lung 

 tissue." 



Mr. W. L. Goodwin, of the School of Mining, Kingston, 

 Canada, has sent us the results of experiments made to deter- 

 mine the relative opacities of various substances to Rontgen rays. 

 The only details as to the method employed is that the results 

 were obtained " by photography with a small Crookes' tube 

 similar in shape to a radiometer, but constructed to show the 

 revolution of a platinum vane covered on one side with mica." 

 The relative opacities thus determined are as follows : — 



I. SoLins :— 



Transparent : Paraffin wax, wood charcoal, coke (in part), 

 asphalte, albertite, starch, diamonds. 



Fair ly transparent : Citric acid, jet, anthracite, amber, natro- 

 lite, caustic potash, caustic soda, borax, so<la crystals. 



Somewhat transparent : Silicified wood, Kpsom salts, ser- 

 pentine, staurolite, stilbite, lazulite, Hj(NH4)P04, cryo- 

 lite, Mohr's salt, analcite, Na-jCO^, borax glass, nitre, 

 Rochelle salt. 



