﻿CLAYS FROM LUZON. 435 



radioactivity was observed in clay number 32, while a certain amount 

 might have been lost from the other samples during the time inter- 

 vening between the taking of the sample and its examination in the 

 laboratory. However, it seems more probable that there may be prac- 

 tically no radioactive bodies in these Islands, for two reasons, first, 

 according to Elster and Geitel, very little radioactivity exists near 

 the sea and, second, matter dissociates under the influence of radiant 

 energy. The tropical sunlight affords opportunity for the maximum 

 effect of the latter. Le Bon ;!T calls attention to the fact that radiant 

 energy falling upon matter causes it to dissociate, and if it is of suffi- 

 cient intensity to heat the substance it also causes an expulsion of a 

 small quantity of the radioactive elements produced by the dissociation. 

 The action of the intense tropical sunlight for centuries on the various 

 deposits occurring here may be accountable for the almost entire absence 

 of radioactivity in these Islands. In support of this suggestion attention 

 is called to the work of Ramsay and Spencer 3S where the "fatigue of 

 metals," a perhaps comparable phenomenon, is produced by the action 

 of intense light. It should also be remembered that Bacon 30 found 

 no radioactivity in the waters of the crater lakes of Taal Volcano. 



S7 Compt. Rend. Acad. d. sc. (1906), 143, 647. 



38 Philosophical Mag. (1906), 12, 402. 



30 This Journal, Gen. Sci., Sec. A (1907), 2, 115. 



