THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



APRIL 1875. 



XXIX. On the Comparison of some Tube and other Spectra with 

 the Spectrum of the Aurora. By J. Hand C apron, Esq., F. G. S.* 



[With Four Plates.] 



o 



IN a contribution by the late Professor Angstrom to the 

 solution of the problem of the aurora-spectrum (an abstract 

 of which appears in * Nature ' of the 16th July, 1874), the Pro- 

 fessor is stated, amongst other things, to have Taid down certain 

 propositions in substance as follows : — 



1st. That the aurora has two different spectra — the one com- 

 prising the one bright line in the yellow-green only, and the 

 other the remaining fainter lines. 



2ndly. That the bright line falls within a group of hydro- 

 carbon lines, but does not actually coincide with any prominent 

 line of such group^ and that Herr VogePs finding this line to 

 coincide with a not well-marked band in the air-spectrum must 

 be regarded as a case of accidental coincidence. 



3rdly. That moisture in the region of the aurora must be 

 regarded as nil, and that oxygen and hydrogen Q must alone there 

 act as conductors of electricity. Professor Angstrom then de- 

 tails the examination of an exhausted dry air-flask filled with 

 a discharge analogous to the glow of the negative pole of a 

 vacuum air-tube, and, comparing this with the aurora-spectrum, 

 gives the following results : — 



Aurora-lines, wave-lengths 4286 4703 5226 

 Violet light, „ 4272 4707 5227 



Two weak light bands found by Herr Vogel at 4663 and 4629 



* Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 49. No. 325. April 1875. S 



