president's address. 25 



oval like an egg spinning on its side; at a still higher speed one 

 end will form a projection which will take the form of a neck 

 with a drop at its outer extremity, and, ultimately, this will be 

 thrown off to form a satellite revolving around the parent body. 

 The beauty and suggestiveness of this scheme become all the 

 greater when we reflect that under such circumstances the 

 original mass must, through the tidal action induced by its own 

 offspring, continually decline in its rate of revolution, and assume 

 a shape corresponding to its changed speed, while the satellite 

 will, through reflex action, steadily increase its distance from the 

 parent body. 



Although we are accustomed to speak of the earth as being 

 practically a rigid body, we must not lose sight of the fact that 

 it is so merely in a comparative sense, and that the hardest rocks 

 of its crust are sufiiciently plastic to permit of the shape of the 

 whole accommodating itself to any change in speed of rotation or 

 indeed to any adequate force continuously applied. The existing 

 equatorial bulge is the result of a definite force due to the period 

 of revolution, and will certainly alter in unison with the gradual 

 decline in the rate of that motion. Gould the revolution of the 

 earth be stopped without disruption through inertia, the equa- 

 torial bulge would disappear in obedience to gravity, and. the 

 earth would become practically globular in shape. 



As will be obvious to all, the extreme interest and importance 

 of the development of the radium hypothesis lies in the great 

 extension of time which it permits for biological evolution and 

 geological development. When we limit the habitable age of the 

 earth by the possible time allowable for cooling from its original 

 heated state, very grave ditficulties arise as to the possibility of 

 fitting in the requirements of geological time; but in the light of 

 the possibilities of radium it is easy to push back the period of 

 gravitational incandescence until the time occupied in cooling 

 from that condition to one in which the existence of life is 

 possible, becomes but a small fraction of the eartli's history. 

 There are, of course, astronomical reasons for placing a limit on 

 the earth's age, but the requirements of astronomy permit of a 



