OBSERVATIONS OF AURORA, FORT RAE, 1882-83. 



General Remarks. 



The aurora was observed hourly, after the magnetic and meteorological observations had 

 been made ; i.e. at from five to ten minutes after each hour. 



No means were available for the instrumental determination of the altitude, &c., of arches ; 

 the information given on these points is by estimation. 



The bearings given are true, not magnetic. 



The situation of the Observatory was not altogether favourable for auroral ol)servations 

 high ground from north to east hiding the horizon to an altitude of 3° or 4° in the direction 

 of the magnetic north. In other directions the view was uninterrupted. 



The brightness is expressed by numerals on the scale to 4. • 5 is rather brighter than the 

 Milky Way. 4 is bright enough to see to read by. 



The general colour of the aurora was greenish-yellow, not unlike moonlight, showing in the 

 spectroscope a single line between the green and the yellow. This line was often visible on 

 overcaBt nights, or when the spectroscope was turned to parts of the sky where no aurora was 

 to be seen. When the brightness reached 1"5, jorismatic colouring frequently showed itself, 

 the lower edge of the arch generally assuming a violet or mauve colour, the upper edge 

 retaining its yellow colour, which however looked at times almost green, pi^obably by contrast. 



On these occasions a faint continuous spectrum and several bright lines appeared towards 

 the violet end of the spectrum. I once saw a bright band in the red. 



It sometimes happened, however, that towards the end of a brillant display of aurora a 

 crimson glow seemed to fill the air below the arch, of which it did not appear to form a part. 

 This colour was very rich and beautiful, and quite different from the colouring of the aurora 

 itself. 



On the few occasions on which aurora was seen by daylight {i.e. after sunset, but before 

 the stars had begun to be visible) it appeared of a pinkish, salmon, or copper colour. 



The type of the aurora, and time of its appearance, was generally much the same on 

 successive nights. 



The displays were as a lule unattended by the slightest sound, but that a peculiar and 

 distinct sound does occcasionally accompany certain displays of aurora, there can be no doubt. 

 The Indians, and voyageurs of the Hudson's Bay Company, who often pass their nights in the 

 open, say that it is not uncommon ; a European who lives in a house may pass a lifetime in 

 the country without hearing it. On one occasion I was fortunate enough to hear it myself. 

 The sound was like the swishing of a whip, or the noise produced by a sharp squall of wind 

 in the upper rigging of a ship, and as the aurora brightened and faded, so did the sound 

 which accompanied it. This proves that the aurora could not have been distant, and I 

 think it possible that these low aurorte may be of a different nature to the high ones. 



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