THORIUM, URANIUM, POLONIUM AND ACTINIUM. 127 



active than the thorium from which it was extracted. 

 This small quantity of very active matter has been called 

 by the discover, Rutherford, thorium X. On examining 

 the thorium X and the precipitated thorium a month 

 later, the astonishing result became evident that the tho- 

 rium X had completely lost its activity while the thorium 

 had wholly regained it; furthermore it was discovered that 

 the rate of decay of the thorium X was exactly equal to 

 the rate of recovery of the thorium. This fact is demon- 

 strated in the diagram (Fig. 41) in which the actual curves 



of decay and recovery are given. The only conceivable 

 explanation of this fact lies in the somewhat extraordinary 

 proposition that the element thorium is constantly generat- 

 ing from itself another solid element, which decays at the 

 same rate at which it is generated. The radio-activity of 

 thorium is due to a balance between two opposing forces 

 which are : (1) the radio-activity resulting from the manu- 



