466 



SCIENCE. 



[N. S. Vol. III. No. 65. 



plate. The tube was but 14 mm. above the 

 coins and 17 mm. above the film. The 

 magnification of the shadows is slight, but 

 the distortion is almost grotesque. Plates 

 showing this effect can be easily obtained. 



It should be stated that the nearness of 

 any conductors, as these coins, to the tube 

 in action will produce in them a consider- 

 able static charge, as may be readily tested 

 by a proofplane and electroscope. This 

 may possibly have a bearing upon the cause 

 of the distortion. 



The rectilinear path of the X-rays after 

 they have passed by an obstacle has been 

 proved by the use of a long strip of cellu- 

 loid film, as used in Kodak cameras. A 

 framework like two parallel ladders was 

 so made that the film could be tightly 

 drawn across the rounds with successive 

 portions parallel and at a distance of 10 mm. 

 from each other, the whole being enclosed 

 in a light-tight box. The X-rays so readily 

 penetrated the gelatine and celluloid that 

 their effect coiild be seen through more 

 than twenty of these equidistant layers. 

 A circular piece of silver was attached to 

 the celluloid side of the front film, and the 

 diameter of its shadow could after develop- 

 ment be quite accurately measured on eight 

 successive layers, although growing diffuse 

 as the distance increased. The ratio of the 

 successive diameters was constant, as would 

 be the case with a rectilinear path. Of 

 course the axis of the ' shadow cone,' given 

 by the position of the circles of the shadow, 

 passes through the source of the rays. On 

 some of the films exposed in this way very 

 curious markings are seen which we are as 

 yet unable to explain. 



This use of films at once suggests the 

 needof a new kind of sensitive plate for pho- 

 tographing with X-rays which shall absorb 

 them far better than does the ordinary dry 

 plate. When a strip of film was folded up 

 on itself, so that there was no loss of in- 

 tensity by increase of distance from source, 



the impression was hardly less strong on 

 the twelfth than on the first layer; and an 

 impression could doubtless be transmitted 

 through a hundred layers. It follows that 

 the time of exposure necessary for X-ray 

 photographs could be diminished in propor- 

 tion as the plates are made to absorb the 

 energy falling upon them. On account of 

 the opacity of platinum, it occurred to me 

 to try platinum photographic paper of the 

 kind used for portraits, but such paper (in- 

 tended for long exposures in printing in 

 sunlight) was far too lacking in sensitive- 

 ness to produce any effect. It ought to be 

 easily possible for our photographic chem- 

 ists to produce plates which should require 

 but one-twentieth or less of the exposure 

 now required for X-rays with ordinary 



The writer has succeeded in repeating 

 Rontgen's reflection experiment, except that 

 a celluloid film was used instead of the less 

 permeable glass plate. Nickel and copper 

 disks were attached to the under side of 

 the film, and after exposure (70 minutes) 

 their effect in reflection was shown by the 

 greater intensity of the dark (or negative) 

 circles above them. 



Certain plates gave anomalous results of 

 reflection, the portion of film above the re- 

 flecting object being affected less intensely 

 than the rest of the film ; that is, the outline 

 of the object beneath the film is shown, but is 

 lighter on the negative than the surround- 

 ing area, instead of darker, as would be ex- 

 pected. 



On four of our plates an appearance 

 strikingly like interference fringes can be 

 observed, and thus far we can only account 

 for it on the supposition of reflection from 

 the brass spring which presses against the 

 glass side of the plate in the holder, thus 

 keeping the plate in place. Numerous at- 

 tempts have been made to obtain interfer- 

 ence fringes after the analogy of Newton's 

 rings, but thus far unsuccessfaUy. 



