242 Causes of the Aurora Borealis. 



But whether it is the identical vapor of the mirage that causes the 

 aurora, is no way material to the argument. The optical phenomena 

 of the higher latitudes, rendei- it probable that an attenuated and di- 

 aphanous medium, different from, and in addition to the air, exists in 

 every place where this phenomenon is apparent.^ 



In the arctic regions the aurora often appears as near and low as 

 many of the clouds. Capt. Parry says, that " distinct layers or stra- 

 ta, seeming to overlap each other, increased the intensity of the light, 

 which at times was something more than the moon in her quarters, 

 dimming the stars, but not concealing them. It was like drawing a 

 gauze veil over that part of the heavens where the aurora appeared." 

 In some instances complete arches or bridges, with well defined 

 edges, arose from a common point, and diverged until 20° apart, 

 when they gradually converged, until they joined in one point in the 

 opposite horizon. f 



Sometimes the streams of light were in right lines like rays ; at 

 others crooked and waving, and moving with inconceivable rapidity ; 

 but the most dazzling corruscations often settled down into a steady 

 arch of yellowish white light. In two or more instances, long dark 

 parallel stripes were noticed, lying horizontally over the arches. 

 These were only separations of the luminous strata, because " the 

 stars were there most plainly visible." These openings prove that 

 the aurora consists of strata or films of vapor ; for the brilliancy of 

 the stars in the dark sky where the light parted, show that the light 



Two persons crossing a tract of salt meadows, a mile or two from the sea shore, saw 

 an immense column before them, reaching from the ground to the clouds : in a mo- 

 ment, anotherof the same dimensions rose, apparently a mile west froni the first, both 

 in the edge of their sensible horizon. These continued unaltered while they rode a 

 mile, stedfastly looking at them, conjecturing them to be water spouts, when they 

 were instantly gone, and an arch of corresponding dimensions occupied their place. 

 The highest point of the arch was about 12°, and was visible a minute and a half 



* The transparency of the aurora cannot be questioned, because the stars are visi- 

 ble through it ; and if the supposed medium exists, it must of course be transparent. 



t White luminous clouds, assuming the precise figures of many of the appearances 

 of the aurora, occurred frequently at Melville Island, occasionally " forming a mag- 

 nificent canopy," as though one section of the heavens was hung in folds of an al- 

 most transparent drapery. 



" The remarkable resemblance of this and many other forms of the aurora to the 

 appearances assumed by the clouds at certain seasons of the year in the polar re- 

 gions, may possibly serve to throw some fight on the nature and peculiarities of the 

 aurora." — Fairy's Voyages. 



