Atmospheric Origifi of the Aurora, t^'c. 155 



tion of the h^'gher clouds, and other obvious crystanizations, than 

 by any periodical diurnal changes. 



The following facts have also an interesting bearing on the the- 

 ory. At Fort Enterprise, where Lieut. Hood found the aurora in 

 one instance to be only 2J miles high, he was, in two instances, 

 surprised to see a discharge of snow, in small flakes, from a clear 

 sky, at times when the aurora was active near the zenith.* 

 These facts, with existing theories, were then extremely puz- 

 zling ; but they are in exact accordance with the above theory. 

 The short interval before the sdow, and the diminutive flakes, are 

 what might be expected in case of an extremely low aurora. 

 Lieut. Hood's^ measurements and observations will not be dis- 

 puted. 



As early as 1820, (April 3,) my interest in the subject of the 

 connection between the aurora and apparent clouds, was excited 

 by a beautiful white arch, like a roll of wool, which on that eve- 

 ning was seen to detach itself from the summit of an aurora of 

 the ordinary character, and in the rapidity of its motion toward 

 the zenith, in the distinctness of its texture as it approached it, in 

 the resemblance of this texture to that of a fleecy cloud, and in 

 . other circumstances, seems to have been unlike any arch in an 

 elevated region. 



•Subsequently, an interesting class of objects of a more deci- 

 dedly nepheological character, but still intermediate between the 

 aurora borealis and ordinary clouds, has presented itself in polar- 

 ized, linear cirri, or magnetic or auroral clouds. The linear cirri, 

 when of great extent, and in other respects of a regular character, 

 have generally been either in or near the magnetic meridian, or 

 nearly at right angles to it. In hundreds of instances, these po- 

 sitions are within a degree or two of them. These can hardly 

 have been accidental coincidences, and they have had no constant 

 relation with wind. In epochs marked by auroras, these have 

 been more marked. They are occasionally composite, consisting 

 of an arch with rays, like streamers. Whence the polarity of 

 these clouds? They open an interesting field, and establish a 

 curious analogy between the aurora and the phenomena of the 

 lower regions. Although the N. and S. delicate lines corres- 

 pond with auroral streamers, in their coincidence Avith the meri^ 



* See appendix to Franklin's Journey to the Polar Seas, 



