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



used by us is that ours calls for a Lick of symmetry about 

 the 180-degree axis. This lack of symmetry appears in the 

 experimental results, and, being a point of some importance, 

 we have established it with some care by a series of obser- 

 vations for the complementary openings 30 degrees and 

 330 degrees over a long range of illumination, as shown in 

 fig. 6. These observations were made alternately with 

 each angle at each illumination with complementary opaque 

 r ota tin o- disks. 



The next point to occupy our attention was the slope of 

 the critical frequency-log I lines for various angular openings. 

 Data obtained by us on several occasions are shown both in 

 the figure just referred to and in fig. 7. While there are 



Fig. 7. 



% 

























30"/ 



/ 









/ IBO^f / 





/ 



/'^ooy 











/ A 



*/ 



/ 





X 



345°/ 











A 





; 







A 







/o 





7 ■*■, 







y 



y 



A \ 









log I 



Critical frequency-log I data for various white angular openings, 

 showing no systematic relation between angular opening aud slope. (The 

 different sets, because obtained under different conditions, are to be com- 

 pared only for slope, and not for relative magnitude of frequencies.) 



differences in the slope of certain of these lines, and while 

 as well the region covered by experiment is too short to 

 establish the presence or absence of some systematic difference 

 of slope, it is clear that there are no such variations of slope 



