Intelligence and Miscellaneous Articles. 529 



into a developing-bath behaved as if unexposed. A prolonged 

 development did not bring out a trace of an image of the lead star. 

 It will be remembered that Prof. Rontgen found that the #-rays 

 penetrated easily through a book of 1000 printed pages. Indeed 

 Gr. Moreau has recently stated that in his hands the #-rays had 

 penetrated through " several metres" of cardboard*. So that the 

 above experiment seems to be very significant. 



2. A piece of sheet aluminium 1*2 millim. thick was accurately 

 fitted into a frame. A very sensitive plate was placed behind it 

 aud a lead star in front. With three hours' exposure not a trace 

 of an image could be obtained. This experiment was varied by 

 substituting thin aluminium-foil for the plate, also by using 

 bromide-paper as the sensitive surface. No images in any case 

 were obtained. 



3. The sun's rays or some portion of its radiation passes readily 

 through wood if the latter is not too thick. Thus, through a piece 

 of white pine r 3 ^ of an inch thick, images that could readily be 

 developed were obtained by three minutes' exposure to afternoon 

 sunlight. With half an hour's exposure the images were brilliant. 



A panel about 12 inches square was removed from an inside 

 shutter and replaced with a piece of white pine | inch thick. 

 When the room was thoroughly darkened, reddish light could be 

 seen to pass through the board. So that wood of this thickness is 

 plainly translucent to the sight. 



The sun's light may be examined for #-rays also by fluorescence. 



4. The panel just described was replaced by one of stout book- 

 board. With the sun shining on this book-board directly and not 

 through glass, paper marked with a saturated solution of barium 

 platinocyanide exhibited no indications of fluorescence when placed 

 behind the board. 



5. Three thicknesses of Bristol-board were pasted together, a 

 circle was cut out, to one side of which barium platinocyanide was 

 applied. The circle was then placed in a pasteboard tube (an 

 arrangement, I believe, proposed by Prof. Magie). When the sun 

 was looked at through this tube the barium salt exhibited fluor- 

 escence. But the interposition between the card and the sun of 

 very thin aluminium-foil sufficed to cut off the fluorescence. 



These concurrent results seem to indicate the absence of arrays 

 from sunlight. 



Charles Henry* quotes an opinion of H. Poincare that all 

 bodies whose phosphorescence is sufficiently intense emit in 

 addition to luminous rays the ar-rays of Rontgen, whatever may 

 be the cause of their fluorescence. Henry quotes confirmatory 

 experiments of his own made with zinc sulphide. 



It seemed worth while to ascertain if this principle is of general 

 application. A dilute solution of uranin was exposed to sunlight, 



* C. R. cxxii. p. 238: quoted Chem. News, Feb. 21, 1896, p. 85 

 (No. 1891). 

 t C. R. cxxii. p. 312 ; Chem. News, Feb. 28, 1896, p. 98. 



Phil. Mag. S. 5. Vol. 41. No. 253. June 1896. 2 



