Prof. A. S. Herschel on the Spectrum of the Aurora. 69 



Positions and General Characters of Principal Lines in the Auroral 



o 

 Spectrum, according to Angstrom. 



Red . . 1. Brightness to 4 or 8. Wave-length 6300. 



Belative position. Atmospheric absorption-line 

 a near C in the solar spectrum. 



General description of source and frequency . Seen 

 chiefly, if not only, in red auroras ; a clearly 

 defined line, sometimes intense ; no other red 

 line visible. 



Identification with lines of electrical air-spectra. 

 Coincides with a red band in the negative- 

 glow discharge. 

 «. Brightness 25. Wave-length 5570. 



Position. Second separable line in the first or 

 citron band of blue gas-flame spectrum. 



Description §c. The most characteristic auroral 

 line; constant and conspicuous in all auroras ; 

 not divisible ; sharp and bright. 



Identification fyc. Not identified; possibly a 

 phosphorescent or fluorescent light emitted 

 when air is subjected to the action of electrical 

 discharge. 



"3. Brightness 2 or 0? to 6 Wave-length522o. 



3 a. „ 



Yellow 

 or citron- 

 green. 



Greenish 



blue or 



blue. 



5170-5190. 



Full blue 



0-8 (increases 1 

 with red line) J " 



3 b. „ 2 or 0? to 8 „ 5000. 



3 c. „ 0to4? „ 4820-4870. 



Position. 3 and 3 a closely adjoin the solar line 

 b and the second or green band of the blue gas- 

 flame spectrum. 3 b is at \ (b, F) ; and the 

 line or lines 3 c are near F. 



Description fyc. The first three are distinct lines ; 

 the first most frequently observed ; the second 

 and third less commonly ; lines in the fourth 

 place (3 c) noted by Alvan Clark, jun., Barker, 

 and Angstrom. 



Identification fyc. 3, 3 b coincide with lines in 

 the negative glow, 3 b that of nitrogen in the 

 nebulae ; Sa with a constant strong line in the 

 spark- discharge. The latter and 3 c, it may 

 be, are only seen in auroral streamers of low 

 elevation. 



Brightness^ (fainter* Wave4 th 4665 _ 474 0. 

 with red line) ) * 



„ 4630-4665. 



■I 



