BY THE EEV. E. F. WHEELEH, M.A. 401 



of Orion : it presented ordinarily a somewhat hazy appearance, 

 but at times would flash out sharply and well defined. It was 

 difficult to make any accurate measurement of its position, but 

 two approximate measures v/ere taken by illuminating the field 

 suddenly by means of a hand lamp, and placing the cross wires 

 as nearly as possible on the position in which the line had been 

 seen. These two estimations are respectively 19-40 and 19"25 

 revolutions of my scale, and place the line between the solar 

 lines D and E ; or very nearly half-way between D and b. 



" The two conspicuous pairs of lines near D in the air spec- 

 trum would be represented on my scale by the numbers 17'89 

 and 18*61 revolutions; but I cannot believe that the two afore- 

 said estimations are so much in error as to render it possible 

 that the latter of these lines is the one seen in the spectrum of 

 the aurora. I am therefore led to the conclusion that the spec- 

 trum of the aurora is not identical with that of air, but as some 

 doubt may exist on this point, I shall anxiously await the next 

 appearance of an aurora to verify this result. The advanced 

 season, however, renders it unlikely that an opportunity will 

 occur for some months ; I have therefore thought it right to 

 communicate my present results, however imperfect they may 

 be. 



" It may be worthy of remark, that the line in the aurora 

 spectrum agrees closely with that of the more conspicuous of 

 the lines in the spectrum of a Orionis, between the solar line D 

 and E. I have measured this line upon two occasions, February 

 12th and 13th, and the resulting measures were 19"35 and 19"38 

 revolutions respectively. There is also a tolerably eonspicuou« 

 line in Aldebaran, near the same place. It is also necessary to 

 state that all these measurements have been referred directly to 

 the Sodium line D, by the observation of the spectrum of the 

 metal from the salt with an alcohol flame, both before and after 

 the observations. They are thus strictly comparable." 



In the course of the discussion which followed on the reading 

 of this paper Mr. Huggins stated that the same single line had 

 been seen by Struve in Russia, about April last year, who found 

 it not only in auroras of which the light was white, but where 



