1865.] 27 [Marsh. 



It is evident, however, that the same peculiarity of position would 

 require that the length of the base line, and, consequently, the 

 height, should be somewhat increased for Newburyport and Bruns- 

 wick, and diminished for Newburyport and Montreal. 



Another arch, seen on the evening of February 21, is thus noticed 

 by Robert Treat Paine, of Boston, in the " Daily Evening Travel- 

 ler," of the 22d : 



" At half-past 8 o'clock, bright branches of white auroral light ap- 

 peared in the N. W., and also in the N. E., which at 8h. 45m., ran 

 together, and formed a luminous arch from N. W. to N. E., the 

 centre of which passed a few degrees above the pole star. The arch, 

 however, was of short duration, as it continued only three or four 

 minutes, and at ten minutes before 9 o'clock, the aurora had entirely 

 disappeared." 



H. D. Vail, at Philadelphia, carefully noted at 8h. 15m. (8h. 31m. 

 Boston time), the position of the upper margin, its highest point being 

 halfway between Gamma Ursae Minoris and the horizon, or at an ele- 

 vation of about 13|°. He did not continue his observations, but at 

 8J o'clock (8f , Boston time), William Dennis, at Germantown, esti- 

 mated its altitude at 15°. 



As Mr. Vail reports the arch seen by him to have been regular 

 and complete, it is evident that the break existing north of Boston 

 at 82 o'clock, was too far east to be visible at Philadelphia, and what 

 Mr. V. saw must have been far to the N. W. of Boston. 



Mr. Paine informs me that his attention having been mainly di- 

 rected to the N. E., he is unable to speak confidently as to the exact 

 location of the auroral branch in the N. W.; he has, however, 

 marked on a star chart his impressions as to the positions at 8 J and 

 8f o'clock respectively, showing a probable altitude for the highest 

 point, of 42° for the former, and 50° for the latter. 



The above altitudes, 13 j° and 42° combined, give the height at 

 8h. 30m. Boston time, 64.8 miles; at 15° and 50° combined, at 

 8h. 45m. Boston time, 66.2 miles. 



While the extreme closeness of agreements in these results for 

 January 16, and February 20 and 21, is, of course, accidental, the 

 average height (66f miles), seems fairly entitled to weight as a 

 rough approximation, and in the present state of our knowledge, 

 even such are valuable. 



The results in this case agree with most others on record in indi- 

 cating that it is only in auroral displays of the very first class that, in 

 our latitude, at least, the "arch," or "curtain," is at a less height 



