428 Mr. Dalton on the Height of the Aurora Borealis. 



was broadest in the zenith, and it was more condensed in the 

 eastern extremity than in the western. Another parallel arch 

 appeared about 20° north of the former, of rather less intense 

 light ; and the northern horizon was luminous as usual on such 

 occasions. After ten minutes or more, the arches advanced 

 each of them to the south 20° with their centres. The ap- 

 pearance lasted about half an hour. A few streamers were 

 seen in the east, which moved slowly northward. Mr. Mar- 

 shall thinks the appearance would have been splendid if the 

 moon had not shone at the time : a halo round the moon va- 

 nished when the bow approached it. I observed a halo round 

 the moon at Manchester that evening. 



Mr. Buchan, a gentleman accustomed to meteorological ob- 

 servations, had mentioned his having seen a similar arch at 

 Manchester on that evening ; but apprehending it might only 

 have been a local phenomenon, I did not inquire particulars 

 till I received the above account from Kendal. Mr. Buchan 

 informs me he saw a luminous arch that evening, about nine 

 o'clock ; the arch was highest to the west of the meridian, and 

 its altitude was very nearly the same as the north pole, just 

 under which it passed ; he estimates it at 53°, and thinks it 

 could not be above 1° more or less. As this observation was 

 not contemporary with that at Kendal, nothing certain can be 

 deduced from them ; but it may not be amiss to observe that 

 an object in the zenith at Kendal, and elevated 53° from the 

 north at Manchester, must be nearly one hundred miles high. 



The results of this series of additional observations agreeing 

 so nearly with that of the 29th of March 1826, I am induced 

 to believe that these luminous arches of the aurora which oc- 

 casionally appear, stretching from east to west, are all of the 

 same height, and that height about one hundred miles. What 

 length the upright beams, — or to speak more properly, those 

 parallel to the dipping needle, — may be, which are the ordi- 

 nary forms of the aurora, we have not observations to deter- 

 mine. Whether those beams arise above the arches, as from 

 a base, or whether they descend below, as if appended to the 

 arches, we cannot absolutely determine. It is remarkable 

 that the arches and beams should rarely, if ever, be seen cog- 

 nate or in juxta position, but always in parts of the heavens at 

 a considerable distance from each other. 



Manchester, March 18, 1828. 



P.S. — Query, Are the parallel bands usually about 20 de- 

 grees asunder ? If so, their distance from each other will be 

 about thirty-six miles. 



LXX. On 



