tresident's addkess. 13 



radiuii), and it would seem that the large new credit on the bank of time 

 given to biologists in coiisequence of its discovery has a definite, if remote, 

 limit. With the quantities of radium at present available for experiment, 

 the amount of loss of particles is so small, and the rate so slow, that it 

 cannot be weighed by the most delicate balance. Nevertheless it has 

 been calculated that radium will transform half of itself in about fifteen 

 hundred years, and unless it were being produced in some way all of the 

 radium now in existence would disappear much too soon to make it an 

 important geological factor in the maintenance of the earth's temperature. 

 As a reply to this depreciatory statement we have the discovery by 

 Rutherford and others that radium is continually being formed afresh, 

 and from that particular element in connection with which it was dis- 

 covered — namely, uranium. Hypotheses and experiments as to the details 

 of this process are at this moment in full swing, and results of a momentous 

 kind, involving the building-up of an element with high atomic weight l)v 

 the interaction of elements with a lower atomic weight, are thought by some 

 physicists to be not improbable in the immediate future. 



The delicate electric test for radio-activity has been largely applied 

 in the last few years to all sorts and conditions of matter. As a 

 result it appears that the radium emanation is always present in our 

 atmosphere ; that the air in caves is especially rich in it, as are 

 underground waters. Tin-foil, glass, silver, zinc, lead, copper, platinum 

 and aluminium are, all of them, slightly radio-active. The question has 

 been raised whether this widespread radio-activity is due to the wide 

 dissemination of infinitesimal quantities of strong radio-active elements, 

 or whether it is the natural intrinsic property of all matter to emit 

 Becquerel rays. This is the immediate subject of research. 



Over and above the more simply appreciable facts which I have thus 

 narrated, there comes the necessary and difficult inquiry, What does it all 

 mean ? What are the Becquerel rays of radio-activity ? What must we 

 conceive to be the structure and mechanism of the atoms of radium and 

 allied elements, which can not only pour forth ceaseless streams of intrinsic 

 energy from their own isolated substance, but are perpetually, though in 

 infinitesimal proportions, changing their elemental nature spontaneous! v, 

 so as to give rise to other atoms which we recognise as other elements "« 



I cannot venture as an expositor into this field. It belongs to that 

 wonderful group of men, the modern physicists, who with an almost weird 

 power of visual imagination combine the great instrument of exact 

 statement and mental manipulation called mathematics, and possess an 

 ingenuity and delicacy in appropriate experiment which must fill all who 

 even partially follow their triumphant handling of nature with reverence 

 and admiration. Such men now or recently among us are Kelvin, Clerk 

 Maxwell, Crookes, Eayleigh, and J. J. Thomson. 



Becquerel showed early in his study of the rays emitted by radium 

 that some of them could be bent out of their straight path by making them 

 pass between the poles of a powerful electro-magnet. In this way have 



