64 



Proceedings of the Royal Irish Academy. 



Fig. 6 shows the graph of the variation of the nuclei with time. The 

 number per c.c. falls off very rapidly at first, but the rate of diminution 

 diminishes with the concentration. The rate of disappearance and its nature 

 preclude any possibiliiy of explaining it by a simple fall under gravity. 

 The nuclei are so small that de Broglie' was unable to distinguish them witli 



1100- 



1030 



300 



800 



700 



600 



X 



P 



500 



400 



300 



200 



100 



40 BO IZO 160 



M i n u tes 



FiG. 6. 



200 



240 



the ultra-microscope, and consequently the amount.of their fall would be quite 

 negligible in the time considered in the experiment. A feasible explanation, 

 however, may be based on the coalescence of two nuclei colliding with sufficient 

 energy, such a collision accounting for the disappearance of one nucleus. 



1 De BrogUe : " Comptes Beudus," vol. 148, 1909, p. 1317. 



