Measurement of the Ohl'njuity Factor of Diffraction. 625 



determined from the measurements of the sectors. Table V. 

 illustrates the method. 



Table V. 



Chords of 

 small Sectors. 



Chords of 

 large Sectors. 



Scale-Readings. 



1-60 

 1-69 

 1-67 

 1 55 

 162 

 1-63 



4-10 

 4-10 

 4-10 

 4-15 

 4-10 

 414 



(a) — 7'55 



(b) = 4-85 



(c) = 5*15 



(d) = 4-57 

 (a+by/ 2=6-20 



(a + b) / 2- c = 1-05 



Mean 

 1 -63 



Mean 

 4-12 



{a + b)l 2-^=1-63 



Observed illumination ratio = 



4-12 

 1-63 

 1*6? * a 



2-53. 



—7-^ ) =2*41. 

 1-05/ 



The results of measurements made on this plan over a 

 pretty wide range of incidences are shown in Table VI. 



Table VI. 



Ratio of Illumination 

 according to the 

 ordinary theory. 



Ratio of Illumination 

 actually determined. 



Ratio of Illumination 



calculated from 



obliquity. 



100 

 100 

 1-00 

 100 

 100 

 100 

 100 



1-48 

 172 

 244 

 2-53 

 3-01 

 3-89 

 4-88 



1-44 

 1-81 

 2.02 



241 

 3-18 

 4 00 

 510 



Total 



1995 



20-16 







