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SCIENCE PROGRESS 



a half days on the average. Radium A springs from the 

 emanation and its average life is shorter still, some three or 

 four minutes only. From A spring in turn radium B and 

 radium C, each of these living about twenty minutes on the 

 average. If therefore, as Rutherford showed, radium were 

 purified of its products and left to itself, the descendants would 

 be present in full force in a few days. In addition to these 

 short-lived products there are succeeding generations ; but the 

 first of these has an average life of some forty years and since 

 it is only manifest in its death, it and its successors give us an 



to«-vi-5»c» t"»orx , 



Fig. 5. 



effect which is comparatively negligible. Lastly radium, the 

 emanations, RaA and Ra C all emit particles but Ra B does 

 not. The bulk of these brilliant deductions of Rutherford's 

 can be illustrated by our experiment. Clearly we can account 

 at once for the four sets of corpuscular radiations ; they must 

 be four lots of a particles from the four substances which emit 

 them and no doubt if we proceed further we shall be able to 

 assign each lot to its own source. But in the meantime we can 

 see a clear proof of a very important feature of Rutherford's 

 theory. When the short-lived products are present in full, they 

 exist in such quantity that the number of atoms of each coming 



