June 4, 1896] 



NATURE 



position, the current was switched on for one minute ; at the 

 end of this time the appearance of the discharge in the tube 

 showing that the latter was growing cold, the current was 

 switched olV, the spirit-lamp again applied to the tube with the 

 right hand, the operator's left hand being kept rigidly in position 

 over the plate, then the current put on again for a minute, and 

 so on, the spirit-lamp and current alternately, till six and a half 

 minutes' (the current at the last time ran a minute and a half) 

 exposure had been given. The plate was then removed and 

 developed uncut, with a hydroquinone developer, with the result 

 that whilst the far denser backgroiiiid of llic last exposed half of 

 the plate shvioed that it had received by far the greater amount 

 of radiant energy from the heated tube during its six and a 

 half minutes' exposure, only the very faintest traces of the 

 bone shadow could be made out in the very bold shadow of 

 the flesh of the fingers ; and on the other half, which had 

 received but one minute's exposure to the cold tube, images 

 iif the bones were very clearly shown. This experiment 

 proves that the radiation received from the hot tube resemble 

 the rays hitherto called X rays (which I have called Xj) in 

 being able tu pass through paper opaque to ordinary light, but 

 differ from them in being unable to jiass through flesh, and in 

 other ways, an account of which must be postponed for a short 

 time. The effect of cooling the X-ray tube is being investi- 

 gated. 



I have spoken of these rays as a new kind of X rays. They 

 may Ije related to the Xj rays in the same kind of way as red is 

 related to violet light, and if so are not essentially different. 

 1 lence I could think of no better nomenclature than to retain 

 the letter X for them, and call them provisionally X.^ ; but ij 

 they have the power of penetrating aluminium at all, they 

 certainly act in some respects so difterently from the Xj rays, 

 that one might feel inclined to suspect them of some greater 

 difference than the fluorescent and photographic experiments 

 indicate. 



Plant Structure Re-oealed hy Rontgen Kays. 



Mr. George J. Burch sends the following account of 

 experiments from the University Extension College, Reading : — 



Since February 13, I have been engaged, in conjunction with 

 my colleague Mr. Dodgson, and Messrs. Ilerbeit, Hooper, 

 Soper, Twiney, West and Vetts, in a series of experiments 

 with Riintgen rays. In investigating the influence of colour 

 upon the relative opacity of certain substances, it occurred 

 to Mr. West to compare a purple hyacinth with a piece of 

 purple glass which had proved remarkably opaque. I found 

 upon development that details of the structure ol the flower were 

 distinctly visible. Following up this clue, we have photographed 

 a number of flowers with the Rontgen rays. By suitably arrang- 

 ing the exposure and the development, we can show the ovules 

 inside the ovary in an unopened bud, the seeds within a seed 

 vessel, and even the veins upon the white petal of a flower. 



-Apparently these results are due to refraction and reflection of 

 the rays when the incidence is sufficiently oblique. Similar 

 indications are visible in a photograph of a fish's eye prepared 

 by Mr. Vetts, in which there is a narrow dark shadow that can 

 only be due to internal total reflection. The feathers are seen in 

 a bird by Mr. Soper, and a foot, developed by Mr. Herbert, 

 shows the fabric of the stocking. 



I am directing the experiments with the view of photographing 

 the soft tissues of the human body. 



A Photometer for Rontgen Rays. 



All those who have had occasion to use Crookes' tubes 

 to produce Rontgen rays will have noticed the extraordinary 

 variations in the intensity of the radiation ^produced by an ap- 

 parently trifling change in the vacuum and the make and break 

 of the coil. .\ useful step towards some quantitative measure- 

 ment of the intensity of Rontgen rays has been made by M. 

 Meslin, who, in the current number n( {.he fournal de Physique, 

 gives an account of a photometer for the ray.s. The principle on 

 which this photometer depends is the matching of the brilliancy 

 of the two halves of a circular patch of liarium-platino-cyanide, 

 one half l)eing rendered fluorescent by Riintgen rays, and the 

 otherrendered.fluorescent by the light rays proceeding from .some 

 standard source, such as a candle or lamp. The light is passed 

 through a coloured glass, so that the fluorescence produced has 

 the same tint as that produced by Rontgen rays. The author 

 finds that the barium-plalino-cyanide, under the influence of 



NO. 1388, VOL. 54] 



Rontgen rays fluoresces with a light of such a colour that the 

 maximum brilliancy occurs for a wave-length of about 0-500 ,u. 

 The barium-platino-cyanide fluoresces most strongly when ex- 

 posed to light having a wave-length of about 0'46oft. By means 

 of this arrangement the author has been able to verify the law 

 that the intensity varies inversely as the square of the distance, 

 the following numbers being obtained : — 



Distance of photometer. mm. mm. 



From luminous source 350 ... 410 



From source of Rontgen rays 54 ... 63 



Quotient, 

 0-853 

 0S57 



The Fluorescence of Photographic Plates. 



As recently stated in Nature (ante p. 62), it is well 

 known that a photographic dry plate exhibits fluorescence when 

 Rtintgdn rays fall upon it. With reference to this, Mr. Shelford 

 Bidwell believes the seat of the fluorescence appears not to be 

 in the sensitive film, but entirely in the glass support. Writing 

 under date May 27, he says : — 



I find that bromide, iodide and nitrate of silver do not by them- 

 selves show the slightest trace of fluorescence, neither does photo- 

 graphic gelatine ; bromide paper and coated celluloid sheets are 

 also quite invisible under Rontgen radiation. On the other hand 

 almost any specimen of glass will, with a good tube, fluoresce 

 sufliciently to show coins in a purse &c. ; indeed, some of the 

 pieces that I tried happened to be more efficient than any of the 

 ordinary dry plates that were at hand. 



No doubt certain photographic plates — possibly those used by 

 Mr. Walker — are for special purposes prepared with fluorescent 

 substances, and it is not surprising that such should fluoresce 

 more strongly than others. 



Miscellaneous Observations. 



From the Sitzungsberichte der Kaiserlichen Wiener Akademie 

 we learn that Prof. G. Jaumann has investigated the deviation of 

 kathodic rays produced by electrostatic force. The rays follow 

 the lines of electrostatic force, and such forces produce a strong 

 deviation in the rays. This deviation is a temporary effect, 

 which is soon brought to an end by the lengthening of the rays. 

 Simultaneously with this electrostatic deviation of the kaihodic 

 rays, considerable variations take place in their intensity. 



The similarity between the effects of Rontgen rays and ot 

 ultra-violet light on electrified bodies, forms the subject of a paper 

 communicated to the .\cademy of Bologna by Prof. .A.ugusto 

 Righi, in which the author considers the influence of the 

 pressure of the gas surrounding an electrified body on the 

 discharge of its electrification produced by these r.ays. It 

 appears that, under similar conditions, the critical pressure (that 

 is the pressure of the gas corresponding to the maximum leakage) 

 is greater for Rontgen rays than for ultra-violet rays. But the 

 final charge of a conductor exposed to Rontgen radiations was 

 found by Prof. Righi to increase with diminishing pressure of 

 the surrounding air precisely as occurs when ultra-violet rays are 

 brought into action instead. In another paper (.Atti R. Accad. 

 Lined), the same writer dissents from Prof. J. J. Thomson's 

 opinion that every dielectric becomes a conductor when it is 

 traversed by Rontgen rays. Prof. Righi is of opinion that it 

 cannot be considered as proved that a non-gaseous dielectric is 

 rendered a conductor when it is traversed by these rays. 



While recently experimenting with a Crookes' tube, Prof. 

 Francis E. Nipher observed that the circular aluminium disc of 

 the kathode became slightly loose on the aluminium wire, and 

 that it was constantly rocking in rotary motion on the wire. 

 After several days of use, during which it had been decided to 

 construct a tube with discs capable of rotation, the kathode disc 

 suddenly became loosened, and began to rotate slowly on the 

 wire as an axis. The direction of rotation was contrary to the 

 hands of a clock, when the disc was viewed from the point 

 where the kathode wire pierces the wall of the tube. When the 

 loose disc was made the anode, no tendency to rotation was 

 observed. Up to May 4, when Prof. Nipher read a paper on 

 the phenomena before the St. Louis Academy of Science, all 

 attempts to produce the effect in air of ordinary pressure had 

 failed. The experiment seemed to form a basis for imposing a 

 term representing a rotation into the equations for force and poten- 

 tial within a wire conductor : but in a letter received a few days 

 ago. Prof. Nipher suggests that a circular or elliptical vibration 

 of the kathode wire might possibly account for the rotation of 



