THE TRANSFORMATIONS OF ELEMENTS 535 



anode, while Rontgen rays, undulations in the ether, are projected 

 in all directions. To these three kinds of ray correspond the 

 three radiations which are emitted by radioactive matter. Like 

 the canal rays are the a rays, heavy particles carrying a positive 

 charge ; the /? rays are electrons like the cathode rays ; while 

 the 7 rays strongly resemble Rontgen rays. 



They are frequently emitted simultaneously from active 

 preparations. Two properties allow of their study and 

 differentiation : : 



(1) They behave differently under the action of a magnetic 

 field; 



(2) Different kinds of rays penetrate matter to very different 

 degrees. 



Under ordinary conditions all these rays, like light rays, 

 travel in straight lines. Under the action of a very strong 

 magnetic field the path of the a rays becomes slightly curved ; 

 j3 rays are much more easily deflected, and, moreover, in the 

 opposite direction to a rays — compare the fact that a rays carry 

 a positive charge, /3 rays a negative one ; 7 rays are not deflected 

 by a magnetic field. 



The difference in penetrating power is well shown by the 

 following table (Rutherford, Radioactivity, p. in) : 



These ratios are only approximate ; rays from different 

 material have greatly varying penetrative power. Different 

 substances absorb them in widely different amounts ; the 

 density of the substance is a factor in determining the amount 

 of absorption. 



The radiations — as has been pointed out in Section 1 — 

 produce ions in the gases they traverse; the mechanism is 

 collision. Their ionising power varies very greatly, being 

 roughly the inverse of their penetrability. 



The enormously greater ionising power of the a rays 

 supports the theory that they are heavy particles shot off from 



