64 THE FIGURE OF THE EARTH 



questions which may be difficult to answer ; but in any 

 case it would now appear that Lord Kelvin's view of the 

 earth as simply a hot solid body in process of cooling 

 can no longer be maintained without qualification, and 

 the argument founded upon it as to the age of the earth 

 either ceases to be valid, or must remain in abeyance till 

 an increased knowledge of radium and its distribution 

 enables us to arrive at a definite judgment. 



The possible effect of radium in the sun has also been 

 pointed out ; 3*6 grams distributed through each cubic 

 metre of the sun's volume would suffice to supply for 

 some thousands of years its entire output of heat.* 



The products of decomposition of this extraordinary 

 element have been supposed by Professor Boys to give 

 rise to those things of mystery the tails of comets, t 

 But these steps are only a beginning. Our whole con- 

 ception of the cosmos seems destined to undergo some- 

 thing like a transformation in the growing light of the 

 new discoveries ; while as regards this vexed question of 

 the age of the earth, the least untrustworthy of our 

 estimates would appear for the present to be that founded 

 on the thickness of the sedimentary series. 



* W. E. Wilson, Nature, vol. Ixviii., p. 222, 1903. 

 f C. V. Boys, Presidential Address, Section A. Brit. Assoc., 1903, 

 p. 530. 



