222 Mr. J. N. Lockyer. On the Classification [Jan. 10,. 



r Barker 431 470'5 



. 1 Vogel 469-4 523'3 



89 ' ' ' ] Angstrom 472'0 521-0 



iLemstrom., 426'2 469'4 523'5 



Means ...... 428'6 470'3 522-6 



Violet light ................ 427-2 4707 522-7 



Although this coincidence is rather striking, it must be remembered 

 that there are other strong bands in the spectrum of the negative 

 pole which do not appear in aurora spectra. As mapped by 

 Hasselberg, the spectrum of the negative pole consists of a series of 

 bright flutings shading off towards the violet, the brightest edges of 

 them being at wave-lengths 419'8, 423'6, 427'8, 451-5, 455'4, 459'9, 

 465-1, 470-8, these are all of equal intensities.* (See fig. 16.) 



Capron remarks that " if the violet-pole glow spectrum is to repre- 

 sent the aurora spectrum, it must be under conditions different from 

 those by which it obtains in dry-air vacuum-tubes or flasks at 

 ordinary temperatures " (' Aurora,' p. 126). 



There can, therefore, be little doubt that the aurora spectrum has- 

 nothing in common with the negative-pole spectrum of nitrogen, and 

 that the three close coincidences noted by Angstrom are merely 

 accidental. 



With regard to Angstrom's objection to Yogel's theory that to view 

 the aurora spectrum as a spectrum of air under unknown conditions is 

 inadmissible, we now know that gas spectra are not so invariable as- 

 Angstrom supposed ; but still we have no right to assume that any 

 particular change is possible until we can prove it experimentally, or 

 at the very least, prove an approach to such a change. If we assume 

 that any change may take place in any spectrum, we upset the whole 

 basis of spectrum analysis. 



Comparison of the Aurora Spectrum with the Negative-pole Spectrum of 



Oxygen. 



The negative-pole spectrum of oxygen, as mapped by Schuster 

 ('Phil. Trans.,' 1879, Part I) consists of four broad bands, the two- 

 brightest having the following positions : 



5205-0 1 Brig}ltest part ......... 5255 



5292'o J 



* j Brightest part ......... 5586 



Under great dispersion, these bands break up into series of lines. 



* ' Memoires de 1'Acade'nrie Imperiale des Sciences de St. Petersbourg,' Series 7, 

 vol. 32, No. 15. 



