134 THE NEW KNOWLEDGE. 



all contain small quantities of the strong radio-active ele- 

 ments as an impurity, or that it is the natural intrinsic 

 property of all matter to emit rays ? 



That important question is for the future to decide. Of 

 one thing we may be certain : If all forms of matter pos- 

 sess the power of emitting rays they do so to an exceed- 

 ingly minute degree. Radio-activity, as we are accustomed 

 to consider it, seems to be par excellence the property of 

 the heavy atom of matter. And if in the future new heavy 

 atoms are discovered we may safely predict for them, as 

 an intrinsic property, the possession of radio-activity. 



