228 



SCIENCE. 



[N. S. Vol. III. No. 59. 



an experiment wherein plates of similar 

 thickness of Iceland spar, glass, aluminium 

 and quartz were employed as screens. 

 Then the Iceland spar showed itself much 

 less transparent than the other bodies, 

 though of approximately the same density. 

 I have not remarked any strong fluores- 

 cence of Iceland spar compared with glass 

 (see below, No. 4). 



4. Increasing thickness increases the 

 hindrance ofiFered to the rays by all bodies. 

 A picture has been impressed on a photo- 

 graphic plate of a number of superposed 

 layers of tinfoil, like steps, presenting thus 

 a regularly increasing thickness. This is 

 to be submitted to photometric processes 

 when a suitable instrument is available. 



5. Pieces of platinum, lead, zinc, and 

 aluminium foil were so arranged as to pro- 

 duce the same weakening of the effect. 

 The annexed table shows the relative thick- 

 ness and density of the equivalent sheets of 

 metal. 



Thickness. Relative thickness. Density. 



Platinum -018 mm. ... 1 ... 21-5 



Lead -050 " ... 3 ... US 



Zinc -100 " ... 6 ... 7-1 



Aluminium.... 3-500 " ... 200 ... 26 



From these values it is clear that in no 

 case can we obtain the transparency of a 

 body from the product of its density and 

 thickness. The transparency increases 

 much more rapidly than the product de- 

 creases. 



6. The fluorescence of barium platinocy- 

 anide is not the only noticeable action of 

 the X-rays. It is to be observed that 

 other bodies exhibit fluorescence, e. g. cal- 

 cium sulphide, uranium glass, Iceland spar, 

 rock salt, &c. 



Of special interest in this connection is 

 the fact that photographic dry plates are 

 sensitive to the X-rays. It is thus possible 

 to exhibit the phenomena so as to exclude 

 the danger of error. I have thus confirmed 

 many observations originally made by eye 

 observation with the fluorescent screen. 



Here the power of the X-rays to pass 

 through wood or cardboard becomes useful. 

 The photographic plate can be exposed to 

 the action without removal of the shutter of 

 the dark slide or other protecting case, so 

 that the experiment need not be conducted 

 in darkness. Manifestly, unexposed plates 

 must not be left in their box near the 

 vacuum tube. 



It seems now questionable whether the 

 impression on the plate is a direct effect of 

 the X-rays, or a secondary result induced 

 by the fluorescence of the material of the 

 plate. Films can receive the impression as 

 well as ordinarly drj' plates. 



I have not been able to show experimen- 

 tally that the X-rays give rise to any calo- 

 rific effects. These, however, may be as- 

 sumed, for the phenomena of fluorescence 

 show that the X-rays are capable of trans- 

 formation. It is also certain that all the 

 X-rays falling on a body do not leave it as 

 such. 



The retina of the eye is quite insensitive 

 to these raj^s; the eye placed close to the 

 apparatus sees nothing. It is clear from 

 the experiments that this is not due to want 

 of permeability on the part of the structures 

 of the eye. 



7. After my experiments on the trans- 

 parency of increasing thicknesses of dif- 

 ferent media, I proceeded to investigate 

 whether the X-rays could be deflected by a 

 prism. Investigations with water and car- 

 bon bisulphide in mica prisms of 30° showed 

 no deviation either on the photographic 

 or the fluorescent plate. For comparison, 

 light rays were allowed to fall on the prism 

 as the apparatus was set up for the experi- 

 ment. They were deviated 10 mm. and 20 

 mm. respectively in the case of the two 

 prisms. 



With prisms of ebonite and aluminium 

 I have obtained images on the photogi-aphic 

 plate which point to a possible deviation. 

 It is, however, imcertain, and at most would 



