unrecognized Wave-lengths. 



163 



Arc managed by A. 



Object = determination with the great arc, of the deviation 

 in a rock-salt prism corresponding to a wave-length of 



5xXD 9 =2"-945. 



Spectrum thrown East. 



Deviation 



39° 21'. 



39° 18'. 



39° 15'. 



39° 12'. 



1st series ... \ 

 2nd series . . . < 



1-8] 



1-3 

 1-3 J 



1 0-9 

 -O'Sj 



3-3] 



3-4 

 3-4 J 



0-6] 



1-1 

 1-6 J 



55 



5-4. 



7-5" 



6-3. 



i5-5 

 -6-9 



2-31 



I 2-9 



3-4 J 



1-7) 



1-7 

 1-7 J 



Specteum thrown West. 



3rd series . . . < 

 4th series . . . < 



1-0 



0-7 

 0-4 J 



-0-1] 



0-1 



0-2 J 



2-1 | 



1 2-4 

 2-7 J 



2-31 



1 2-4 

 2-4 J 



4-0 

 3-9 J 



3-4] 



1 3-5 

 3-6 J 



0-2] 

 01 

 -01 J 



-01 1 



Ui 



0-3 J 



The sodium-line of the 5th spectrum fell exactly upon the 

 slit S 2 at the beginning and end of the observation. 



From smooth curves the following positions were deduced 

 for the maximum : — 



O I // 



Spectrum east 39 15 7 



» 39 15 



Spectrum west 39 16 



„ 39 16 4 



Mean .... 39 15 8 



The preceding examples will sufficiently indicate the means 

 used in making the following measurements of wave-length 

 with the grating, which have been carried on continuously 

 from December 1885 to April 1886. As a rule, each of the 

 sixty-two determinations in the following Table represents 

 one or more days' labour, thongh in some cases two or more 

 determinations have been secured in the same day. 



M2 



