THE AURORA. ]<j 



the most singular and interesting properties of light, 

 we find that the earliest determination of the real na- 

 ture of the auroral light or rather of its spectrum 

 was that effected by Angstrom. This observer took 

 advantage of the occurrence of a brilliant aurora in the 

 winter of 1867-'68 to analyze the spectrum of the col- 

 ored streamers. A single 'bright line only was seen ! 

 Otto Struve, an eminent Russian astronomer, shortly 

 afterward made confirmatory observations. At the 

 meeting of the Royal Astronomical Society in June, 

 1868, Mr. Huggins, F. R. S., thus described Struve's 

 results : " In a letter, M. Otto Struve has informed me 

 that he has had two good opportunities of observing 

 the spectrum of the aurora borealis. The spectrum 

 consists of one line, and the light is therefore mono- 

 chromatic. The line falls near the margin of the yel- 

 low and green portions of the spectrum. . . . This 

 shows that the monochromatic light is greenish, which 

 surprised me ; but General Sabine tells me that in his 

 polar expeditions he has frequently seen the aurora 

 tinged with green, and this appearance corresponds 

 with the position of the line seen by M. Struve." 



The general import of this observation there is no 

 mistaking. It teaches us that the light of the aurora 

 is due to luminous vapor, and we may conclude, with 

 every appearance of probability, that the luminosity of 

 the vapor is due to the passage of electric discharges 

 through it. It is, however, possible that the position 



