54 A. W. Steuxirt 07i 



them conduct electricity readily ; they produce photographic 

 effects upon sensitive {)lates, even through cardboard ; they cause 

 zinc sulphide to glow strongly, as is seen in the ordinary luminous 

 watch or compass ; they colour glass violet or brown according to 

 its chemical composition, and they have a powei-ful disintegrating 

 action on vit:d tissue. 



This last property is utilized in radium therapy, which is 

 successful in the case of rodent ulcer and similar diseases. The 

 radio-active material, usually the gas niton, is enclosed in a tiny 

 tu1)e within a silver sheath and introduced into the wound. The 

 violent action of the rays destroys the diseased tissue, and it is 

 possible for fresh healthy tissue to grow in its place. 



There is another property of radium which requires atten- 

 tion. The radium atoms are constantly bi-eaking up, so that, 

 although radium is an " element," it is not a permanent body. 

 Half disappears in 1,350 years, so that in 2,700 years only one- 

 fourth will be present, and in another 1,350 years only one- 

 eighth. If, then, there is now in existence one gramme of 

 radium, and if it be the descendant of a pre-existing mass, this 

 mass, no longer than 140,000 years ago, must have been as large 

 as the earth, a conclusion which all the facts of geology show to 

 be absurd. It must therefore be assumed that radium has a 

 parent, from which it is being continually derived. Just as the 

 gas niton is a descendant of radium, so is radium itself a 

 product of ionium, which is in turn descended from yet another 

 elementary form of matter. 



Thus a certain family relationship among the radio-active 

 elements can be traced, which will be dealt with in the next 

 lecture. 



In conclusion, it seems worth while to draw attention to the 

 immense i)ractical benefits which have followed the investigations 

 in this one fiehl of research, investigations which have their 

 origin in University laboratories, and which were undertaken 

 only from a pure love of knowledge for its own sake. 



