OF THE AURORA BOREALIS. 5 



sometimes meet and span the heavens with an entire arch ; suddenly the columns 

 and clouds of auroral vapor will assume a crimson hue — next, all the columns and 

 streamers will rush towards a point a little southeast of the zenith, corresponding 

 to the pole of the dipping-needle, and wreathe themselves around it in a splendid 

 coronet — and finally auroral waves will begin to flow upward from the horizon 

 towards the same point in surprising undulations, which are often continued a great 

 part of the night. Meanwhile, the magnetic needle is violently agitated, and 

 deflected from its normal position. 



It is the occurrence of these great auroras, repeated with unusual frequency, 

 that constitutes a period like that under review, which I have denominated the 

 Secular Period of the aurora borealis; while auroras presenting some of the 

 humbler forms of the phenomenon, as the northern twilight, or the streamers, are of 

 ordinary occurrence. 



We shall find it convenient to distribute the different forms of the aurora into 

 four distinct classes, with a description of the characters belonging to each class 

 respectively. 



Class I. This is characterized by the presence of at least three out of four 

 of the most magnificent varieties of form, namely, arches, streamers, corona, and 

 waves. The distinct formation of the corona is the most important characteristic 

 of this class; yet, were the corona distinctly formed, without auroral arches or 

 waves, or crimson vapor, it could not be considered as an aurora of the first class. 



Class II. The combination of two or more of the leading characteristics of the 

 first class, but wanting in others, would serve to mark class the second. Thus 

 the exhibition of arches and streamers both of superior brilliancy, with a corona, 

 while the waves and crimson columns were wanting; or of streamers with a corona, 

 or of arches with a corona without streamers or columns (if such a case ever 

 occurs), we should designate as an aurora of the second class. 



Class III. The presence of only one of the more rare characteristics, either 

 streamers or an arch, or irregular coruscations, but without the formation of a 

 corona, and with but a moderate degree of intensity, would denote an aurora of the 

 third class. 



Class IV. In this class we place the most ordinary forms of the aurora, as a 

 mere northern twilight, or a few streamers, with none of the characteristics that 

 mark the grander exhibitions of the phenomenon. 



HISTORY OF THE RECENT SECULAR PERIOD. 



From about the year 1780 to 1827, striking exhibitions of the aurora borealis 

 were very unfrequent, although, probably, more or less of an inferior description, 

 as those of the third and fourth classes, were seen every year, even in our own 

 latitude, and a still greater number in the regions north of us ; but aged people 

 who witnessed the displays of eighteen hundred thirty-five, six, and seven, testified 

 that these were similar to such as occurred in their youth, from 1760 to 1781. 



