known hj the Name of the Aurora Borealis. 177 



for the present to the consideration of those who may take an 

 interest in the subject, if by your favour it shall be presented to 

 thenu 1 am, sir. 



Your obedient humble servant, 



William Dobbie. 



On the Aurora Borealis. 



It has long been a generally received opinion, that the aurora 

 borealis is the exhibition of immense masses of the electric 

 fluid in vacuo, or at least at such a height that the atmosphere 

 is in an extremely rarefied state. No circumstance connected 

 with these phsenomena seem however to favour that opinion, 

 much less to warrant the unreserved manner in which it has been 

 adopted. 



The following questions may be proposed, to show how little 

 is known concerning those phaenomena. 



\Vhy is tlieir appearance confined to particular times of the 

 year and of the night? 



Whv are they always seen in a particular quarter of the 

 heavens ? 



Whv do they in general assume the particular form and po- 

 sition observable, rather than any other ? 



Why are they under all their various appearances different in 

 colour from the electric fluid in other cases ? 



And, lastly. Why is the motion of the electric fluid so dissimilar 

 to that of streamers, tlie former being determined by known 

 laws ; whereas the latter move to and fro laterally, without even 

 a conjecture as to the cause of such motion ? 



Streamers are said to be often accompanied with a hissing or 

 rustling noi-se. This notion probably had its origin at the time 

 when they were supposed to be ominous of disastrous events, or 

 to represent armies in hostile conflict, and might arise from a 

 sympathy of the sense of hearing with that of vision. At least, 

 it would not be easy for our untutored ancestors to conceive how 

 those gigantic aerial warriors could perform their treniemlous 

 evolutions altogether without noise : the latter seems to have 

 been the idea concerning those appearances in the tiaie of 

 Ossian, and in some measure till the present time. 



This wild notion of the hissing and crackling noise has been 

 acceded to bv manv who ought to be more guarded in '.vliat they 

 admit regarding n;itural plueiiomcna, as it is completely at vari- 

 ance with the fundamental part of their own hypothesis, which 

 is, that this peculiar appearance of the electric fluid is produced 

 by the total or partial absence of air. This being granted, how 

 are they to account for the production or transmission of sound? 

 Besides, the hcij>lit generally assigned to streamers is manv times 

 Vol. 5G. No. 2Gy'. Srjjl. 1820.' Z greater 



