RADIOACTIVE CHANGE 117 



CHIEF FEATURES OF RADIOACTIVE CHANGE. 



The features that distinguish radioactive change 

 from chemical change, and which have made it 

 possible in a few short years to reduce to some 

 degree of finality and completeness the intensely 

 complicated series of successive changes suffered by 

 the elements uranium and thorium in the course of 

 their disintegration, are chiefly two. In the first 

 place, the whole phenomena are inevitable, incapable 

 of being changed or deviated from their allotted 

 course by any means whatever, independent of 

 temperature, concentration, or the accumulation of 

 products of reaction, the presence of catalysts, 

 irreversible and capable of being accurately and 

 quantitatively followed without alteration or disturb- 

 ance of the changing system. The mathematical 

 theory, although for many successive changes it 

 becomes cumbrous and unwieldy to a degree, involves 

 only the solution of one differential equation by a 

 device quite within the compass of anyone possessing 

 a knowledge of the bare elements of the calculus to 

 employ. The second feature is in the magnitude of 

 the energy evolved, which, weight for weight of 

 matter changing, surpasses that evolved in the 

 most exothermic chemical changes known, from one 

 hundred thousand to a million times. Manifested in 

 the form of rays, by their fluorescent, photographic, 

 or ionising power capable of being put into evidence 

 in almost inconceivably minute amount, changes are 

 capable of being followed, and by the electroscope 

 accurately measured, which would conceivably require 

 to continue for millions of years before they could 

 be experimentally detected by chemical or even by 

 spectroscopic methods. The disintegration of the 

 single atom is ascertainable, for example, in the 

 spinthariscope of Sir William Crookes, where each 



