718 Messrs. H. E. Ives and E. F. Kingsbury on the 



Substituting values of K x and K 2 , 



F F 



log Ii— ./ -- , T == — log lo - T7— 



(8) 



??i 1 log Ii+pi ^ W2 logI 2 + ^ 2 



This relationship is not capable of simple solution, but 

 upon insertion of numerical values on the left-hand side the 

 value of I 2 may be found by the process of trial and error, 

 its limit being set by the points b and c of fig. 1. 



4. Comparison of Experimental and Calculated Values. 

 After substituting in equation (8 ) values selected from the 

 actual experimental ones and after plotting the calculated 

 figures, it was found that the resulting curves take the 

 exact form shown in fig. 2. 



Fie?. 7. 



* 





! ! 



j 









/A 





/ 





j j 







A 



W / 

















//fy 











1 



i 

























, &y/ 



















yf/ 



















W, 



// 















^^ " 



V 

















lZ34Sf>'[83 



.Loq I 

 Calculated values of quantities of colours to be alternated with the stan- 

 dard to produce the condition of constant summation. Reading horizon- 

 tally from any point on the standard line, the full lines give, by reference to 

 the axis of abscissae, the intensities to give the same critical frequency, 

 the broken lines the intensities to read equal in the flicker photometer. 

 Reading vertically, relative critical speeds for equally bright points are 

 found. 



