1889.] principal Line in the Spectrum of the Aurora. 433 



discusses in detail nearly all the recorded observations of the spectrum 

 of the Aurora from 1867 to 1882, and then brings them together in a 

 table, with such probable errors as the original statements of the 

 observers enabled him to assign to them. I think it is desirable to 

 give that part of his list which contains the observations of the 

 brightest line : 



1867. Angstrom Upsal X 5567 + 1-0 



1868. Struve Poulkowa 5552 + 14'9 



Lemstrom Tromsce 5659 + 14*0 



1869. Peirce iStats Unis 5565 1O8 



1870. Proctor 5595 + 25'0 



1871. Smyth fidimbourg 5579 9'5 



Lindsay Aberdeen 5680 50'0 



Barker New Haven 5594 13'0 



1872. Yogel Kiel 5571 0-9 



Denza Moncalieri 5568 + 11'9 



Donati Florence 5569 lO'O 



Oettingen Dorpat 5548 + 30'0 



Eespighi Rome 5574 lO'O 



Wijkander Spitzberg 5572 + I'O 



1873. Backhouse Sunderland 5660 + lO'O 



Barker New Haven '5569 13'9 



Lemstrom Enare 5569 + 0'5 



1874. Backhouse Snnderland 5570 + lO'O 



Maclear " Challenger " 5522 + 37'1 



1879. Nordenskiold Pitlekaie 5563 lO'O 



1880. Copeland Dunecht 5572 2'0 



1882. Gyllenskiold .... Cap Thordsen .... 5568 1'6 



1884. .... Upsal 5569 + 6'2 



Gyllenskiold then calculates by the method of least squares the 

 mean value of all the determinations, and finds the following 

 result : * 



Mean value of the 23 observations, X 5570'0 + 0'88 (7). 



The recent measures by C. C. Krafft,f depart largely from 

 Gyllenskiold's mean value. Krafft found on 



1882, November 2 A 5595 



11 . 5586 



and measures with the same instrument made by Schroeter on 

 November 17th, gave X 5587. 



* Ibid., p. 169. 



t ' Beobachtnngs-Ergebnisse der Norwegischen Polarstation,' &c. A. S. Steen. 

 Clmstiania, 1888. 



