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Prof. A. S. Herschel on the Spectrum of the Aurora. 71 



as distinguished from 

 the tops of the stream- 

 ers, giving to the sub- 

 spectrum a different 

 appearance according 

 to the strength and 

 agitation of the stream- 

 ers : this may perhaps 

 be traceable in the ap- 

 pearance and disap- 

 pearance of the lines 

 3 a, 3 c, and perhaps 

 of other faint lines, 

 whose positions should 

 be noted. Such lines 

 should also be searched 

 for in quiescent parts, 

 such as stationary 

 auroral bands and the 

 tops of very bright 

 streamers. 



A correct recogni- 

 tion of some one or 

 more of the lines de- 

 scribed above, other 

 than the citron line, is, 

 however, of chief im- 

 portance in observing 

 with small spectro- 

 scopes, as the leading 

 lines themselves must 

 supply the only stand- 

 ard intervals of com- 

 parison for eye-estima- 

 tions of such faint 

 spectra. 



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