Aimospheric Origin of the Aurora, §c. 155 
tion of the higher clouds, and other obvious sepenalanations; than 
by any periodical diurnal changes. 
The following facts have also an sabeendiing bearing on the an, 
ory. At Fort Enterprise, where Lieut. Hood found the aurora in 
one instance to be only 24 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 snow, 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 Hie 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 iortarvating class-of lgeiis ote a more. _ detie 
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 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 ae streamers, in their ae with the meri- 
~* See appendix to. Franklin’s Journey to the Polar Seas, 
