204 G. F. BECKER ISOSTASY AND RADIOACTIVITY 



radioactive. There is even a possibility that radioactive energy has been 

 potentialized at the expense of energy of compression.^" 



It has often been asserted that the discovery of radioactivity indefi- 

 nitely prolongs the probable age of the earth. To me it seems that the 

 determination of the level of compensation limits both the age of the earth 

 and the amount of radioactive matter in its outer shell. 



"" Ascription of the heat of stellar bodies to compression originated with Kant in 1785, 

 not with Helmholtz in 1854. Cf. Bull. Oeol. Soc. Am., vol. 19, 1908, p. 130. 



