84 THE KINGDOM OF MAN 



of radium, we have the evidence of enormous quantities 

 of radium in the sun, for we know helium is there in vast 

 quantity. Not only that, but inasmuch as helium has 

 been discovered in most hot springs and in various radio- 

 active minerals in the earth, it may be legitimately argued 

 that no inconsiderable quantity of radium is present in 

 the earth. Indeed, it now seems probable that there is 

 enough radium in the sun to keep up its continual output 

 of heat, and enough in the earth to make good its loss 

 of heat by radiation into space, for an almost indefinite 

 period. Other experiments of a similar kind have ren- 

 dered it practically certain that radium itself is formed 

 by a somewhat similar transformation of uranium, so that 

 our ideas as to the permanence and immutability on this 

 globe of the chemical elements are destroyed, and must 

 give place to new conceptions. It seems not improbable 

 that the final product of the radium emanation after the 

 helium is removed is or becomes the metal lead ! 



It must be obvious from all the foregoing that radium 

 is very slowly, but none the less surely, destroying itself. 

 There is a definite loss of particles which, in the course 

 of time, must lead to the destruction of the radium, and 

 it would seem that the large new credit on the bank of 

 time given to biologists in consequence 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 



