36 Mr. J. N. Lockyer. On the Wave-length of the [May 2. 



merits of the chief aurora line which he made with considerable dis- 

 persion in 1874, but which have never before been published. As the 

 position determined by him differs from the approximate wave-length 

 of the manganese fluting, which, so far as I know, had only been pre- 

 viously given by Lecoq de Boisbaudran,* I have deemed it desirable to 

 redetermine the wave-length with increased dispersion. For this 

 purpose a 4-prism Steinheil spectroscope was employed, the wave- 

 lengths being determined by comparison with the solar spectrum and 

 Angstrom's map. 



Manganese 

 (Lockyer) . 



o Sodium 

 (Angstrom) . 



Aurora 

 (Huggins). 



Fig. 1. — Diagram comparing the manganese fluting with the aurora line, the D lines 

 being also shown for comparison. 



The result of the observations with increased dispersion, which were 

 made by my assistant, Mr. Fowler, is shown in the diagram, from 

 which it will be seen that the wave-length of the most refrangible 

 edge of the first fluting which is not perfectly sharp, is about 5576. 

 The wave-lengths of all the details of the fluting shown are — 



r 55 76 Most refrangible edge. 



Mn (1) < kpqo \ Double maximum. 



5589 J 



^5604 Another maximum. 



Taking the mean of the values of the aurora line quoted by Dr. 

 Huggins, viz. : — 



Yogel, 1872 5571-3 + 0'92 



Huggins, 1874 5571-0 ± 0*5 



Gyllenskiold's mean, 1867-1884 . . 5570-0 ± 0-88 



we get 5570-76 + 0'76. This gives the limiting values as 5571*5 and 

 5570-0. 



* 'Spectres Lumineux,' p. 116. 



