THE AURORA BOREALIS. 



737 



18. Comparison of other Spfxtra with the Aurora Spectrum, 

 by J. R. Capron.— (Phil. Mag., April 1875.) 



For comparison with a table of Aurora spectra given in 

 M. Wijkander's paper (see p. 742), a table of the results obtained 

 by other observers, as given by J. R. Capron, is added, together 

 with the spectra of hydrogen and oxygen (Vogel), and carbon 

 (Dr. Watts and J. R. Capron). 



Aurora Lines and Bands. 



Observers. 



Green. 



Blue. 



Violet. 



Vogel, April 9, 



1871. 

 Barker, Nov. 



9, 1871. 



Barker, Oct.") 

 14,1872 -i 



A. Clarke, Oct. 



24, 1870. 

 Backhouse, 



1873. 

 Backhouse, 



Feb. 4, 1874. 

 Hydrogen 



lines. 

 Oxygen lines 



Carbon (Dr. 

 Watts). 



Carbon (Ca- 

 pron). 



629-7 

 623-0 



630-0 

 606-0 



556-9 

 562-0 



555-0 

 569-0 

 566-0 

 557*0 

 555-5 

 560-3 

 562-2 

 560-8 



539-0 



542-2 



533-0 

 532-0 



523-3 



518-9 

 517-0 



520-0 



516-5 

 518-0 

 518-9 

 519-5 

 518-9 

 519-3 



500-4 



502-0 



505-0 



to 

 499-0 



501-5 

 498-0 

 500-8 



469-4 



462-9 



482-0 



493-0 



to 

 485-0 

 485-0 



4S3-0 



483-4 

 482-9 

 482-5 



474-0 



to 

 467 



•o3 



462-5 

 464-0 

 463-2 



431-0 

 435-0 

 430-5 

 432-0 



Mr. Capron generally agrees with the results arrived at by 

 M. Angstrom, but sees reason to question the statement that 

 " moisture in the region of the Aurora must be regarded as nil" 

 Also he sees no reason for giving to the violet-pole glow any 

 special or distinguished place in comparison with the Aurora. 

 He considers that the fainter lines are partly due to the air-spec- 

 tiiim, in which H. lines play a prominent part, and the spark- 

 spectrum appears nearer the mark than the tube-spectrum ; and 

 that the remaining bands or hues (besides the phosphorescent 

 lines) may be due to phosphorus and iron. 



For measuring auroral and other lines, a cheap and very 

 effective micrometer is constructed by making the whole slit- 

 plate of the spectroscope traverse the field with a fine micrometer 

 screw, a pointer or pointers being fixed in the eye-piece. 



Large aperture, both of prisms and lenses, is almost indispensable 

 in observations of faint Auroral spectra. 



19. Observations on the Aurora, by M. Lemstrom. 

 Description of M. Lemstrom^ s Spectroscope, 



On a massive foot is fixed a vertical brass tube ; another brass 

 tube sliding within it carries a strong plate of metal, which can 

 36122. 3 A 



