104 REV. JAMES FARQUHARSON ON THE AURORA B0REALI8. 



Trans. 1828, "On the Height of the Aurora Borealis above the Surface of the 

 Earth ; particularly of one seen on the 29th of March, 1 826." Mr. Dalton in 

 that paper, supposing the same luminous belt was seen on the 29th of March at 

 places distant from each other at the same time, infers its height to have been 

 1 00 miles and upwards. 



If I shall have occasion to differ widely from Mr. Dalton's conclusions, I 

 beg to do so in terms of high respect for that distinguished individual, whose 

 labours have so much benefited science; and whose opinions I shoidd not have 

 ventured to controvert, had I not possessed peculiar advantages for observa- 

 tion ; and liad I not made on one occasion an observation which appears 

 decisive of the question of height, as will be afterwards stated. 



I do not mean to confine myself, however, to the discussion of that question 

 only, but to communicate several very curious results of the numerous obser- 

 vations I have made, which as far as I am able to ascertain are not yet gene- 

 rally understood among men of science. 



I had announced these results in a short paper published in the Edin. 

 Phil. Journ. vol. viii. p. 303, April 1823; they are, "That the aurora bo- 

 realis has in all cases a determinate arrangement and figure, and follows an 

 invariable order in its appearance and progress ; — that the streamers (pencils 

 of rays) of the meteor generally appear first in the north, forming an arch from 

 east to west, having its vertex at the line of the magnetic meridian ; — that when 

 this arch is yet only of low elevation, it is of considerable breadth from north 

 to south, having the streamers of which it is composed placed cross-wise in re- 

 lation to its own line, and all directed towards a point a little south of the 

 zenith ; — that the arch moves forward towards the south, contracting its lateral 

 dimensions as it approaches the zenith, and increasing in intensity of light by 

 the shortening of the streamers near the magnetic meridian, and the gradual 

 shifting of the angles, which the streamers near the cast and west extremities of 

 the arch make with its own line, till at length these streamers become parallel 

 to that line, and then the arch is seen as a narrow belt, 3° or 4° only in breadth, 

 stretching across the zenith at right angles to the magnetic meridian ;— that it 

 still makes progress southwards ; and after it has reached several degrees south 

 of the zenith, again enlarges in breadth, by exhibiting an order of appear- 

 Jinces the reverse of that which had attended its progress towards the zenith 



