Aurora Borealis of November 14, 1837. 287 



their fleeting existence and their mutabihty while they do exist, 

 the great numbers which, in every striking display, commonly 

 spring up and fade incessantly, and finally, the restlessness with 

 which they are momentarily changing their positions, till at 

 length they vanish, are all circumstances precisely suited to con- 

 found all simultaneous observation, and to render it next to im- 

 possible to obtain a parallax. These remarks apply to columns 

 seen laterally. If to both the observers, the Aurora is coronal or 

 vertical, the difficulty becomes still greater. Since the corona 

 seems, every where, to settle itself at a point in the heavens in 

 the hne of the dipping needle, it follows that every place, during 

 a vertical Aurora, must have its own corona, which can be seen 

 from no other position. Were it not so, the distance of the Au- 

 rora might be determined at once ; since the corona, if its appa- 

 rent form were real, would present a most striking object, visible 

 at the same time to a multitude of observers ; while the steadi- 

 ness of its position would afford abundant time for accurate ob- 

 servation. 



There is one mode, and, as it seems to the writer, only one, in 

 which the question admits of being settled. It may, after all, 

 lead only to an approximation to the true altitude of the Aurora j 

 still it may unquestionably determine the limit, beyond which the 

 luminous vapor cannot be. This is to institute a series of obser- 

 vations along the same meridian, in order to determine, as accu- 

 rately as possible, the lowest latitude at which the auroral columns, 

 on a given occasion, reach the zenith. Let an observer, then, situ- 

 ated at any given distance due south, observe the greatest altitude 

 at any time attained by the columns directly north of him, and a 

 parallax may be obtained, by means of which the problem may 

 be solved. For instance, on the occasion we have been consid- 

 ering, a corona was formed at Richmond, Va., and perhaps even 

 farther south. At Culloden, Geo., the greatest altitude observed 

 during the evening, was about equal to that of the pole star. 

 Were these two places on the same meridian, we should be able 

 to say, from knowing their difference of latitude to be 4° 47' 17'' 

 very nearly, that the height of the Aurora could not be much 

 greater than two hundred geographical miles. 



At Society Hill, the greatest observed altitude appears to have 

 been about 40°. A similar calculation founded on this observa- 

 tion, would reduce the extreme height of the Aurora at its sum- 



