138 Capt. Abney. Solar Spectrum. [Dec. 6, 



Description 

 of line. 



X from 

 comparison 

 of 4st and 

 2nd orders. 



X from 

 comparison 

 of 2nd and 

 3rd orders. 



X according 

 to .Fievez. 



Remarks. 



Centre of 



DL 11 pd.ll Ul 



lines in the 

 flutings fol- 

 lowing A. 



7643 -2 



7643 33 



7652-2 





The determination of A has been made by Mascart, Smyth, and 



o ■ 



others, besides Angstrom and Langley, with discordant results. I 



o 



think the above may be taken as accurate as are Cornn's and Ang- 

 strom's maps. 



It may be useful to forestal the detailed publication of my measure- 

 ments by giving the wave-lengths of a few of the principal lines in the 

 infra-red. The scale numbers refer to my map of the infra-red, which 

 is published in the " Phil. Trans.," Part II, 1880. 



Scale number. 



Description. 



Wave-lengths. 



1046 



This line is a triple line, the two"] 







strongest components of which 1 



8226 -4 1 





hare the accompanying wave- f 



82*9 -9 J 









1441 





8496 -8 



1509 





8540 6 



1685 





8661 -0 



2175 



A double line, the components"! 



8986 -2 \ 

 8989-5] 





of which have the accompany- j» 







2638 



9494 -5 \ 

 9500 -1 J 



3161 





9633 -8 



The measurements of the lines have been made with a micrometer 

 by Hilger. The tu^oo °f an inch can be easily measured, and in 

 extreme cases the to-oWo of an inch can be recognised. 



