SUCCESSION OF CHANGES IN RADIOACTIVE BODIES. l7l 



matter undergoes two successive changes in thorium and actinium and at least four 

 successive changes in radium. 



The changes occurring present several points of interest and importance and will 

 l>e considered in some detail. In the course of this jwper the following subjects 

 will be considered : 



1 I ) Nomenclature ; 



(2) Rate of decay of the excited activity of thorium and radium for different 



times of exposure to the emanation, and for the different types of 

 radiation ; 



(3) Mathematical theory of successive changes; 



(4) Application of the theory to explain the changes in () thorium, 



(6) actinium, (c) radium ; 



(5) Matter of slow rate of change produced by radium : comparison of the 



matter with the radio-tellurium of MAKCKWALD ; 



(6) Apparent radioactivity of ordinary matter, due in part to an active deposit 



of slow rate of change from the atmosphere ; 



(7) Comparison of the successive changes in uranium, thorium, actinium, and 



radium ; 

 Table of active products ; 



(8) Discussion of the significance of rayless ' changes in the radio-elements. 



(9) Radiations from the active products ; 



Significance of the appearance of and y rays in the last rapid change in 

 the radio- elements ; 



(10) Difference between radioactive and chemical change ; 



(11) Discussion of experiments made to measure the charge carried off by the 



a rays ; 



(12) Magnitude of the changes occurring in the radio-elements; 



(13) Origin of the radio-elements. 



4. Nomenclature. The nomenclature to be applied to the numerous radioactive 

 products is a question of great importance and also one of considerable difficulty. 

 Since there are at least six distinct substances produced from radium, and probably 

 five from thorium and actinium, it is neither advisable nor convenient to give each a 



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