SYMPOSIUM OX RADIOACTIVITY. 57 



period varies very greatly for different elements. For uranium 

 it is estimated at 6.000,000,000 years, for radium 1,760 years, for 

 radium emanation 3.86 days, while for the actinium emanation it 

 is only 3.9 seconds. 



Recognizing that in radium emanation we have a source of 

 energ}' of an entirely new order. Ramsay conceived the bold idea 

 that it might be made use of to bring about the disintegration of 

 other elements, and in 1P07 he announced that potassium and 

 lithium may be formed by the action of radium emanation on 

 copper. A repetition of his experiments by Madame Curie has, 

 however, thrown some doubt upon this conclusion. 



The discovery of radioactiv-ity has opened up to the vision of 

 chemists a whole new field of work and has introduced many 

 new points of view in the science. It has also given very strong 

 support for the much older notion that there is some sort of 

 genetic relationship among the chemical elements. It has com- 

 pelled us to revise our definition of elements and compounds, and 

 to recognize that what we have called an atom is in some cases, 

 and probably always, composite. The last ten years have brought 

 such varied and startling discoveries, in bewildering rapidity, that 

 it seems certain that we are only at the threshold of a new epoch 

 in the physical sciences. 



IV. 



THE BEARINGS OF R-\DIOACTIVITY OX GEOLOGY.* 



By Thomas Chrowder Chamberlin. 



University of Chicago. 



To the geologist interest in the phenomena of radioactivity 

 centers in the spontaneous evolution of heat that accompanies 

 atomic disintegration. This interest is the more piquant because 

 the source of the internal heat of the earth is one of the oldest of 

 its problems and the discover}- of radioactivit}- brings into the 

 study an unexpected element. During the last centur}- there was 

 a rather general consensus of opinion that the earth's internal heat 

 was derived from the condensation of the nebula from which the 

 earth was then commonly supposed to have taken its origin. This 

 nebula was usually regarded either as a gaseous body or as a 

 quasi-gaseous meteoritic swarm, and in either case its condensa- 



iThe discussion before the Academy was extemporaneous and this paper written 

 oat long after is only a substitute. — T. C. C. 



