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A Description of several extraordinary Displays of the Aurora 

 Borealis, as observed at Prestwich, during the winter of 

 1848-1849 ; with Theoretical Bemarks. By William 

 Sturgeon, Lecturer on Natural and Experimental Philo- 

 sophy, formerly Lecturer at the Honourable East India 

 Company's Military Academj', Addiscombe, and late Editor 

 of the " Annals of Electricity," &c. Communicated by 

 the Author. 



(Concluded from page 158.) 



Theoretical Views. 



With i-espect to the cause of this meteor, I can form no other 

 opinion, than that it originates in a sudden change of temperature 

 in the upper regions of the atmosphere, whicli gives rise to a corre- 

 sponding disturbance of the electric fluid, causing extensive move- 

 ments of it amongst the attenuated air and aqueous vapour, illumi- 

 nating them as it spreads in various directions, according as their 

 different parts are prepared for its reception and diffusion. It is no 

 unusual circumstance to observe preparations as it were, during the 

 evening, before daylight has disappeared, for a display of auroral 

 beams or streamers after nightfall. These preludes consist of certain 

 arrangements of thin streaks of nubiferous matter, floating at high al- 

 titudes, and often stretching quite across the heavens, and appearing 

 to converge at two opposite points near the horizon ; forming what 

 some people call Noah's Ark. These streaks or bands of vapour, 

 when traversed by the electric fluid at the night time, become lumi- 

 nous conductors, and form streamers of the aurora borealis ; display- 

 ing diflferent degrees of brilliancy, in correspondence with the atten- 

 nalion of the nubiferous arrangement and the quantity of electric fluid 

 flowing through it. From this simple fact, which I have myself 

 witnessed, and from the high probability that similar arrangements 

 of still more attenuated aqueous vapour are frequently formed at al- 

 titudes where they are far beyond the reach of observation, until illu- 

 minated by electrical disturbances, there can appear no great degree 

 of exti'avagance by supposing that most, if not all, streamers assume 

 their peculiar forms from a like cause. It is possible, however, that 

 on many occasions, the electrical disturbances may take place even at 

 higher altitudes, and the light be transmitted through the thinnest 

 bands of these nubiferous arrangements, which would give the ap- 

 pearance of streamers or luminous beams, as decidedly as if they 

 were themselves the conductors or channels of electrical transmis- 

 sion. 



The streamers, which mostly constitute a conspicuous feature in 

 the aurora borealis, are not often suddenly formed ; they generally 



