906 



Mr. W. J. Harrison on the 



A curve has been drawn showing the relation between 

 logo- and the number of days since the beginning of the 



•9500 



•9000 



•8500 



7500 







N 



























\ 





































\ 

































































30 40 



50 60 70 



NO. OF DAYS. 



90 100 110 l?0 



130 



experiment. From the curve it is found that the activity 

 falls to half value in 148 days. This differs slightly from 

 the initial value which is given by Mme. Curie as 140 days, 

 but the accuracy of the experiment is not sufficient to justify 

 any deduction therefrom. 



I have to thank Prof. Strutt for suggesting this experiment 

 and for the loan of the polonium. 







XCVI. The Decay of Waves in a Canal. By W. J. Harrison, 



M.A., Fellow of Clare College, Cambridge *. 



IN Dr. Houstoun's reply f to my paper % it is clearly evident 

 that his main contention must be wrong. It is necessary 

 lor the validity of his argument that waves of the type 



and those of the type 



sin - — sin -j^- 

 o 



. qirx riry 

 sin - — cos -=-£• 

 o 



a o a 



should have different periods and rates of decay (moreover, 



that waves of the type sin I — cos —^ 

 J r a b 



should have the same 



* Communicated by the Author. 



t Phil. Mag. [6] vol. xix. pp. 205-206 (1910). 



X Phil. Mag-. [6] vol. xviii. pp. 483-491 (1909). 



