166 



Prof. S. P. Langley on 

 Table (continued). 



o 



ff) 03 



o 



0Q 





1 





£ 

 8 



1 



■"£ a 



© 03 



r^ a? 



Mean De- 

 viation, re- 

 duced to 

 60°. 



Ph a 









O / // 



o 



O < // 



O / II 





Arc 



7xAD 2 = 

















4-1231 



1 



59 57 45 



15 



39 02 18 

 01 48 

 00 30 



) 













23-8 



02 00 

 01 36 



00 48 



01 42 



>39 03 42 

 ±12" 



1-5215 

 ±•0001 









»J 



„ 



00 42 



) 





Arc 



8xXD 2 = 

















47121 



1 



59 57 45 



15 



38 51 18 

 50 48 

 52 12 

 54 42 

 54 42 

 54 12 



> 

 .38 56 06 



1-5201 











a 



±30" 



±•0002 









5> 



J5 



57 36 

 55 18 



/ 





Arc 



9xXD 2 = 

















5-3011 



1 



59 57 45 



15-4 



38 45 12 

 45 42 



1 











>» 



? , 



47 12 



}>38 48 06 



1-5186 









V 



» 



48 48 



+30" 



±•0002 









" 



" 



47 18 





In the following brief Table we have summarized the results 

 of all this labour. Our working method gave the index in 

 terms of the wave-length ; but since ordinarily the former is 

 the known and the latter the unknown quantity, we here 

 give the mean probable error as finally corrected as a function 

 of the latter. 



Given Indices of Refraction 

 in Rock-salt Prism. 



1-5442 

 1-5301 

 1-5272 

 1-5254 

 1-5243 

 1-5227 

 1-5215 

 1-5201 

 1-5186 



Wave-lengths 

 from Direct Observation. 



(a) by the eye ; 



(b) by the bolometer. 



XD 2 = 0'5890±0'000 (a) 



2x\D 2 = M780±0-002 (b) 



3xXD 2 = l-7670±0005 „ 



4 x\D 2 = 2-3560 ±0-009 „ 



5xXD 2 = 2-9451±0-013 „ 



6 xXD 2 = 3-5341 ±0-019 „ 



7xXD 2 = 4-1231±0-029 „ 



8xXD 2 = 4-7121±0-043 „ 



9 xXD 2 = 5-301 1+0-065 ,, 



