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The Emanations of Radium. 



[Mar 17, 



neither screen showed any light. Over the radium the platino 

 cyanide screen showed a very luminous disc, corresponding with the 

 opening of the crucible, but the blende disc remained quite dark. 



It therefore appears that practically the whole of the luminosity 

 on the blende screen, whether due to radium or "polonium," is occa- 

 sioned by emanations which will not penetrate card. These are the 

 emanations which cause the scintillations, and the reason why they 

 are distinct on the blende and feeble on the platinocyanide screen, 

 is that with the latter the sparks are seen on a luminous ground 

 of general phosphorescence which renders the eye less able to see the 

 scintillations. 



Considering how coarse-grained the structure of matter must be to 

 particles forming the emanations from radium, I cannot imagine that 

 their relative penetrative powers depend on difference of size. I 

 attribute the arrest of the scintillating particles to their electrical 

 character, and to the ready way in which they are attracted by the 

 coarser atoms or molecules of matter. I have shown that radium 

 emanations cohere to almost everything with which they come into 

 contact. Bismuth,* lead, platinum, thorium, uranium, elements of 

 high atomic weight and density, possess this attraction in a high 

 degree, and only lose the emanations very slowly, giving rise to what 

 is known as " induced radio-activity." The emanations so absorbed 

 from radium by bismuth, platinum, and probably other bodies, retain 

 the property of producing scintillations on a blende screen, and are 

 non-penetrating.] 



It seems probable that in these phenomena we are actually wit- 

 nessing the bombardment of the screen by the electrons! hurled off 

 by radium with a velocity of the order of that of light ; each scin- 

 tillation rendering visible the impact of an electron on the screen. 

 Although, at present, I have not been able to form even a rough 

 approximation to the number of electrons hitting the screen in a given 

 time, it is evident that this is not of an order of magnitude incon- 

 ceivably great. Each electron is rendered apparent only by the 

 enormous extent of lateral disturbance produced by its impact on the 

 sensitive surface, just as individual drops of rain falling on a still 

 pool are not seen as such, but by reason of the splash they make on 

 impact, and the ripples and waves they produce in ever-widening 

 circles. 



* I have been quite unable to detect any lines but those of bismuth (and of 

 known impurities) in the spectrum of the strongest and most active " polonium" 

 salt I have been able to procure. 



f Radiant matter, satellites, corpuscles, nuclei ; whatever they are, they act like 

 material masses. 



