124 Transactions. — Miscellaneous. 



the invisible rays. One step more — a simple piece of wire 

 placed between the ' window ' and the plate— and Lenard 

 would have obtained a shadow photograph similar to those 

 obtained a few weeks later by Eontgen." 



It is certainly singular that, even by accident, Lenard 

 should not, during the course of those experiments, have dis- 

 covered the peculiar property which some at least of the 

 invisible rays, the existence of which he had ascertained, 

 possessed, of throwing the shadow of any substance which 

 absorbed them upon the fluorescent screen. This was the 

 result of the further step taken by Eontgen. 



It seems that his researches were being carried on upon 

 somewhat different methods from those adopted by Lenard,- 

 and the experiment which led to the discovery of the rays in 

 question, as distinguished from the other kathode rays, is thus 

 described : " Having made a Crookes's or Lenard's tube glow in 

 the way already mentioned, he surrounded it with a close- 

 fitting shield of blank paper, and when the light from the 

 glow was thus effectually intercepted, and the room completely 

 darkened, he found that a paper covered on one side with 

 barium platino-cyanide lit up with brilliant fluorescence when 

 brought into the neighbourhood of the tube, precisely as if a 

 ray of sun or arc light had been thrown upon it. It at once 

 became evident to him that the effect produced was due to 

 the presence of rays differing from those which were inter- 

 cepted by the black paper in which the tube was wrapped, and 

 what was especially remarkable was that they made the 

 fluorescent screen shine, even at a distance of 6ft. from the 

 covered tube." A full account of his experiments, translated 

 from the German, appeared in Nature, of the 23rd January, 

 1896, and contams a statement of many of the facts that have 

 been published in the ordinary Press, showing the force with 

 which these dark rays penetrate solids. Boards, books, blocks 

 of ebonite, and other substances quite opaque to the rays of 

 the sun or other light-rays, proved to be as transparent to the 

 X rays as glass is to the visible rays. A plate of aluminium 

 half an inch thick was penetrated by them, and they appear 

 to be only effectually resisted by comparatively considerable 

 thicknesses of the heavier metals. When, however, a human 

 hand was interposed between the darkened tube and the 

 screen a shadow was seen, showing the bones darkly, with 

 only faint outlines of the surrounding soft tissues ; but, amidst 

 all the recorded experiments with these rays, I have searched 

 in vain for the mention of any attempt to determine whether 

 they are, and, if so, to what extent, intercepted by the com- 

 binations of orange and yellow glass used to prevent the action 

 of the ordinary actinic rays upon a sensitized photographic 

 plate. But whatever interest attaches to Eontgen's discovery 



