SUCCESSION OF CHANGES IN RADIOACTIVE BODIES. 205 



these elements gives rise to a gaseous product, the emanation, aud this in turn is 

 transformed into a type of matter which is deposited on the surface of bodies. In 

 both thorium and radium, the fourth change is followed by a change in which all 

 three types of rays appear together, while the third product in all three elements 

 does not emit rays at all. The remarkable similarity in the nature of the changes 

 occurring in radium, thorium, and actinium, indicates that the constitution of the 

 atoms of these bodies is very similar. 



The time T taken for each product to be half transformed, and the value of the 

 related constant \, the fractional amount of the product changed per second, are 

 shown in the following table, together with some of the physical and chemical 

 properties of the products : 



