Mr. J. Glaislier on the Aurora Borealis. 369 



of the meteor was visible at these points, and appeared round, 

 and certainly not less than 15' in diameter, — I should say 

 double that measure. I was in some degree enabled to judge 

 by estimating, after it had passed, the size of the gaps in the 

 clouds where it was fully visible. The light was very great, 

 enabling me to see surrounding objects as plainly as during a 

 vivid flash of lightning, and lasted about two seconds. 



Now to compare my observation with the diagram and 

 notice sent you last year by Sir J. Lubbock, I conclude he 

 must have seen the meteor just before its disappearance; in 

 which case, the course being very much foreshortened, it 

 would occupy the portion of the heavens which he has indi- 

 cated by a blurred mark of his pencil. On this hypothesis it 

 must have passed about 8° or 10° from the zenith of his place 

 of observation, which I suppose to be in longitude 0° 4-'*5 W., 

 lat. 51° 20' N. 



1 consider then that the meteor at the end of the phoeno- 

 menon bore N. by 10° W. at Sir J. Lubbock's station at 

 an altitude of about 40°; at my station at the same instant it 

 bore N.E. at an altitude of 45°. From these data, I calculate 

 its height to have been sixty-one miles nearly. 



But taking its course as upon a meridian line, and the esti- 

 mated altitude when due east of me, I make its height about 

 fifty-six miles. Considering the roughness of the data, I re- 

 gard this degree of accordance, proceeding upon two inde- 

 pendent methods, as tolerably satisfactory. Then, if my esti- 

 mate be at all correct, it had a diameter of at least 700 yards, 

 and its velocity was thirty-six miles in a second. 

 I remain, Gentlemen, 



Your obedient servant, 



John Slatter. 



LXL On the Aurora Borealis, as it isoas seen on Su7iday 

 eve?iijig, October 24, 1847, at Blackheath. By James 

 Glaisher, Esq., of the Royal Observatory, Greenwich, 



THIS day having been remarkable for one of the most 

 brilliant displays of Aurora Borealis which it has ever 

 been my good fortune to witness, it has occurred to me that a 

 notice of its principal phases, so far as they fell under my own 

 observation, may not be unacceptable to your readers. 



The barometer reading during the day previous had de- 

 clined rapidly, and during this day it had increased as rapidly. 

 The day had been for the most part overcast, and light rain 

 had fallen occasionally ; towards evening the sky became per- 



Phil, Mag. S. 3. Vol. 31. No. 209. Nov. 1847. 2 B 



