98 



MR. JOHN BURKE ON THE CHANGE OF 



In each of the experiments one or more of the cubes was shaded from the 

 fluorescence-producing light. The letter in the fifth column indicates which was 

 that protected. 



Experiments (a). 



Similarly taking in all eighty observations for a, ft, and ft /(I -f a), the following 

 are obtained, the fixed slit being at 8 : 



Hence 



therefore 



Also we easily obtain 



and 



8 , 0-03 



* 



= 1-449 [1 0-005] ; 



a = 0-449 0'005. 



ft = 0787 0-006 



= 0-521 0-006. 



It may be remarked that the probable error in a is much less than that in ft or 

 ft/(l + a). My attention was called to this when revising the paper. A glance at 

 figs. 3, 4, and 5 will make this clear. The light emanating from a^ and a\ will 



