150 Mr William Sturgeon 07t the Aurora Borealis. 



companying the aurora borealis tlian any other attempt at explana- 

 tion hitherto on record. The observations were made whilst walk- 

 ing from Brixton to my residence in Pomeroy Street, Old Kent 

 Road. 



" The sky was partially covered with thin vapoury clouds, which 

 had an obvious influence on the colour, and the apparent horizontal 

 motion of the light, which was easily discerned to be behind or be- 

 yond these thin clouds of vapour, and assumed a deeper tinge of red- 

 ness as the vapour became more dense between it and the spectator. 

 As this was the first time of my observing a red light during the 

 display of an aurora borealis, I became anxious to know the cause, 

 for I never saw the electrical light, in artificially-attenuated air, any 

 thina like the colour of the lioht which I observed on this occasion. 

 It was sometimes of a deep crimson, at other times of an almost 

 fiery red; then pink, very light pink; next the yellowish- white 

 colour which the aurora most usually displays ; and so on for sevei-al 

 alternate successions. At other times the aurora would seem to re- 

 verse the order of colours, beginning with the white light, and pass- 

 ing through the different red tints down to a perfect crimson, and 

 then return gradually to the ordinary white. I had several oppor- 

 tunities of observing the curious changes of colour in the aui'oral 

 light before I arrived at Camberwell. Just before I entered the 

 Grove, at Camberwell, then about half-past nine o'clock, the northern 

 sky was illuminated, througliout an immense horizontal range, with a 

 rich red light ; but when I arrived at the churchyard, about five 

 minutes afterwards, the red light had nearly disappeared, a small 

 portion only remaining on the northern edge of a thin fleece of va- 

 pour, at a considerable height above the western horizon, being suc- 

 ceeded by several fine groups of the usual white streamers."* 



On this occasion I had an excellent opportunity of observing that 

 the red light never appeared when the sky was pretty clear of those 

 thin vapoury clouds ; which frequently skimmed across the aurora 

 and I eventually became so perfectly convinced of the effects they 

 produced on the colour of the light, that I could predict the appear- 

 ance of the red colour by observing the approach of the thin fleeces 

 of vapour, before coming within the limits of the aurora. From 

 these facts, it would appear that the prismatic colours which occa- 

 sionally adorn the aurora borealis, are secondary phenomena, pro- 

 duced by the ordinary decomposition of the original light, and need 

 not be looked upon as any thing extraordinary beyond the certainty 

 of an abundance of aqueous vapour, either in the rerrion of the elec- 

 trical disturbance, or at a lower altitude in the atmosphere. 



But to return to the aurora of the 27th October. The luminous 



* Annals of Electricity, &c., vol. iv., p. 403. 



