Atmospheric Origin of the Aurora^ Sj'c. 149 



The following is a summary. 



' That crystals of snow more minute and simple than those 

 which occasion halos, and usually too minute to produce sensible 

 opacity, are always present in the atmosphere, above the region 

 of ordinary clouds, during the time of this meteor, we are indu- 

 ced to believe from a comparison of the results of the foregoing 

 observations. Several of these results are believed to be new. 

 The following are some of the circumstances which have a bear- 

 ing upon this question. 



1st. Those seasons of the year and those hours of the night 

 when it most frequently occurs, are favorable both to the presence 

 and congelation of aqueous vapor in the atmosphere. 



2d. The clearness. of the sky, which at such times is usually 

 either general or total. 



3d. The usual northerly breeze at the earth's surface, and the 

 northeasterly breeze in the high region of the meteor. 



4th. The usual depression of the temperature, at those heights 

 at which thermometrieal observations are made. 



5th. The clouds which usually succeed the meteor immediately 

 or on the same evening, and which often present the appearance 

 of being continuous and identical with the auroral matter. 



6th, The snow that in weather sufficiently cold, almost uni- 

 versally follows the meteor, after such an interval as the sim- 

 ple crystals might be expected to require for aggregation in more 

 complicated groups and descent to the earth's surface. 



7th. The rain that almost universally succeeds it, after about 

 the same interval, whenever the temperature of the lower atmos- 

 pheric strata is sufficient to melt falling snow. 



8th. The co-existence of halos with regular crystals, the con- 

 nexion between halos and auroral clouds, and between auroral 

 clouds and vertical lunar columns, and the analogy between au- 

 roral clouds and the aurora borealis. 



9th. The pinnate appearance of composite auroral clouds, which 

 appear (so to speak) like large crystals.' 



From this point, the author, not finding any former theory of 

 the aurora not liable to great objections, has ventured into the 

 regions of speculation, and in relation to the intimate nature of 

 the phenomenon, and under the 4th head, of views of a more 

 hypothetic class, has ventured to inquire whether atmospheric 

 crystallizations may not occasion the development of auroral 



