20 



of the transition of a quantity from the + to the — affection, which 

 the author conceives to be illustrative of his general design. 



December 8, 1845. 



On the Heights of the Aurora Borealis of September 17 and 

 October 12, 1833. By Professor Potter, A.M., of Queen's College. 



The data for the calculations are almost entirely taken from the 

 conspectuses of the observations printed and distributed in 1833 by 

 the British Association ; and although so long time has elapsed, no 

 calculations of the heights of the phenomena, which are the first 

 steps to be taken in finding the nature of the meteor, have, to the 

 author's knowledge, been hitherto published ; the only imperfect 

 discussion being given in the Philosophical Magazine for December 

 1833. 



The observers of the display of September 1 7, were Mr. J. Phil- 

 lips, at York ; Mr. Clare, Mr. Hadfield and the author, at or near 

 Manchester ; Professor Airy, at Cambridge ; and the Hon. C. Harris, 

 near Gosport. 



The observers of that on October 12, were Professor Sedgwick, at 

 Dent; Mr. W. L. Wharton, near Guisborough ; Mr. J. Phillips, at 

 York ; Mr. Clare, Mr. Hadfield and the author, at or near Man- 

 chester ; Dr. Robinson, at Armagh ; Professor Airy, at Cambridge ; 

 and the Hon. C. Harris, at Heron Court. 



The observations of the aurora of September 17 at Cambridge at 

 8 h 25 m Greenwich time, taken with those at Manchester at 8 h 24 m , 

 give the height of the lower edge of the arch 56 English miles, and 

 of the upper edge 7 1 miles. 



The observations of another arch, seen from 10 h 49 m to ll h 19 m 

 at York, and from 10 h 49^ m to ll h 4| m near Gosport, give the 

 height of the lower edge 389 miles. 



The observations on October 12, at 7 h 56 m at York and at 7 h 54 m 

 at Cambridge, give the height of the upper edge of an arch 72*2 

 miles. 



The observations at Guisborough at 8 h 20 m , and at Heron Court 

 at 8 h 22 m , give the height of the under edge of the arch seen at that 

 time 70'9 miles, and of the upper edge S5"5 miles. 



The observations at Dent at 8 h 55 m , taken with others at Man- 

 chester at S h 54 m , give the height of the upper edge of that arch 

 84-97 miles. 



The last arch remained stationary about a quarter of an hour, and 

 therefore the observations are the more valuable ; but combining an 

 observation at Armagh with those at Manchester, the height comes 

 out only 64'47 miles ; and even with the utmost allowable latitude 

 to the deductions from the observations, the height comes out 66'5 

 miles. 



The last arch having been noticed to have risen to a higher alti- 



