II. 



RADIOACTIVITY. 



Bv BERTRAM B. BOLTWOOD. 

 (Read April 22, igii.) 



The study of the discharge of electricity through gases and the 

 properties of radioactive substances has done much to broaden our 

 knowledge of the relations of electricity and matter. It has served 

 to throw a new light on the ultimate constitution of matter itself, 

 and, while confirming the older theory of a discontinuous or atomic 

 structure, has led to the presumption that the chemical atom is not 

 only divisible into still smaller entities, but that in some cases it can 

 undergo a spontaneous disruption accompanied by the ejectment of 

 certain of its constituent parts at high velocities. All this has opened 

 a broad and attractive field for more or less legitimate speculation 

 and conjecture. 



Since the first recognition by Becquerel in 1807 o^ the radio- 

 active phenomena exhibited by the element uranium, the extension of 

 our knowledge of the radioactive substances has steadily and pro- 

 gressively advanced. This development has been due in great part 

 to the early formulation of the theory of atomic disintegration, pro- 

 posed in 1902 by Rutherford and Soddy, which has served as a 

 systematic foundation and has afforded an orderly basis for the 

 interpretation of the otherwise somewhat complicated relations. 



According to this hypothesis the atoms of the primary radioactive 

 elements are considered to undergo spontaneous disintegration and 

 in this manner to give rise to a series of successive radioactive prod- 

 ucts, differing from the parent substances as well as from one another 

 in phvsical and chemical properties and in the relative stability of 

 their atomic systems. Simultaneously with the disruption of the 

 atoms certain characteristic radiations are emitted by ikit systems, 



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