i78 An Attempt tu explain the Phatnomenon 



greater than the distance wliich the loudest known sounds ever 

 reach, even where the niediiun is properly adapted to their pro- 

 duction and transjiiission. 



Havini;- tlms stated the ahove c,i;jections to the prevalent opi- 

 nion lespecting the caii5:e of the aurora bnrecilis, it is the object, 

 in what follows, to endeavour in few words to account for the 

 phaenoinei.a in question, so as to remove the ol;jcctions and fur- 

 nish an^weit; to the questions above stated 



It is generally at or near the time of the equinoxes that those 

 lights make their appearance in these latitudes, at which times 

 the sun's rays would be tangents to the poles of tiie earth, were 

 they not disturbed by the refractive power of the atmosphere. 

 By the refraction, it is obvious that the rays will extend to a cer- 

 tain point beyond the pole, on the side opposite to the sun, when 

 they must of course fall on the immense accumulation of ice 

 within the polar circle, and will be reflected with great brilliancy 

 towards the darkened hemisphere, undergoing in their course 

 another refraction, which bends them still more southward; and 

 as the atmosphere possesses also the power of reflecting light, 

 those rays will finally fall back on the earth, and will at a certain 

 angle and within certain limits be visible to its inhabitants. 



Wliat is here advanced accounts satisfactorily and with sim- 

 plicity for those phaenomeua, and also for the annual and diur- 

 nal times of their appearance. Towards midsummer and mid- 

 winter the relative position of the earth and sun is unfavourable, 

 or rather does not admit of those appearances in our latitude. 

 But further north they may be and are seen during a greater 

 part of the wiiiter. The fact here agreeing so well with the as- 

 signed cause, is a strong evidence that it is the true one. At the 

 seasons above mentioned, several hours after sun-set, when a ver- 

 tical plane passing from us to the centre of the sun would also 

 fall within the limits of the frozen regions of the pole, then, cir- 

 cumstances permitting, streamers might be seen faintly at first 

 towards the east; and as the sun proceeds nearer to the centre 

 of the jjolar regions the streamers advance westvvard, and are 

 more elevated; and if contiuued till near midnigiu,his rays falling 

 on a world of unsullied snow and ice, forming angles of every 

 descrijjtion, shoot forth into our zenith a beautiful though con- 

 fused assemblage of prismatic colours. Towards midnight is the 

 only time, and near the zenith the only place, that I have cer 

 seen coloured streamers : the fact and the theory a2;ree here also 

 60 reuuukably, that a doubt concerning the cause can scarcely 

 be entertained. The time of appearing, and situation in the 

 heavens, of th.ose phaenomcna being thus accounted for, it is easy 

 on the same principle to account for their form and position. 

 The general form of stjeanicrs^ as this name inijjorts, is that of 



a long 



