JOLY — Radiant Matter. 



81 



Let the ray be supposed to move along the line A B — this line representing 

 the range. If at each point of its path we erect a perpendicular line 

 proportional to the number of ions created by the flying helium atom, then, 

 by joining up tlie ends of these lines, we obtain tlie curve shown. It will be 



A 2 4 6 



Eange in cms. of aii'. 



noticed that a very well-defined maximum exists, after which the ionization 

 rapidly drops to nil. The curve reproduced is due to Geiger, who has 

 added considerably to our knowledge of the subject. 



I hold in my hand a small speck of tlie substance, pitchblende — the 

 uranium ore from which radium is derived. All the elements of the uranium 

 series are present. We are sure, then, that every a ray proper to this series, 

 whose ranges are given in the table, is being emitted by this particle of 

 pitchblende. Let us form a mental picture of what is going on around it. 



Furthest out of all, the helium from Ea C is projected. It attains a 

 distance of 7 centimetres. The greater part by far of its ionization is done 

 near the end of its flight. Hence, remembering that these rays are darting 

 radially in all directions from the piece of pitchblende, there is a shell of 

 intense ionization of spherical form existing around this pitchblende and at 

 a distance of between 6 and 7 centimetres from it. This is entirely due to 

 Ra C. Within this shell we have a spherical shell due to Ra A. It is the 

 next we meet as we go inwards. It has an extreme diameter of 4'8 cms. The 

 next shell is created by emanation. Its radius is 4-2 cms. The shell due to 

 Ra F succeeds at 3-8 cms. ; then comes that made by radium, and lastly a 

 very intense one due to the nearly coincident effects of three rays, two due 



SCIENT. PBOO. R.D.S., VOL. XIII., NO. VI. ® 



