G8 
PROFESSOR W. N. HARTLEY AND MR. W. E. ADENEY 
Position of grating when the normal was parallel to 
the incident ray. 51° 3' 18" 
Position of grating when the spectrum was being 
photographed. 42° 22' 25" 
Point on the arc corresponding to fiducial line I. . . 32° 43' 41" 
51° 
3' 
18"- 
0 
1 
22' 
25"=8° 
- 1 
40' 
53' 
42° 
22' 
25"- 
-32° 
43' 
41"=9° 
38' 
44 
B-i 
2 
whence 3=27° 58' 21" 
8 is negative and n is negative, a= ’00146859 
therefore \=4671 , 7 
The constant of the grating was determined by means of the sodium lines 
If and D 2 of the first and second order of spectra on both sides of the regularly 
reflected rays, with the following result:— 
Di. 
D ; . 
First order to the right .... 
0-00146831 
0-00146855 
Second order. 
0-00146858 
0-00146861 
First order to the left. 
0-00146853 
0-00146900 
Second order. 
0-00146861 
0-00146855 
Mean=0’00146859 
The following table gives the wave-lengths corresponding to all the fiducial lines, 
together with their angular measurements. 
