Mr. Harris on the Aurora Borealis. 525 



it was this that induced me to look out ; and I have little 

 doubt, from a similar circumstance mentioned by Parry in his 

 first Tour, that this was the daylight appearance of the Aurora. 



ON THE HEIGHT ABOVE THE SURFACE OF THE EARTH 



OF A LUMINOUS ARCH OF THE AURORA BOREALTS, 



ON THE 7th OF JANUARY, 1831. 



BY S. H. CHRISTIE, ESQ., M.A., F.R.S., &c. 



HPHE height of the Aurora Borealis above the surface of the 

 earth has been so variously estimated, that any observa- 

 vations which determine limits to the height of a particular 

 phenomenon become interesting, although these limits may not 

 be extremely close. The most permanent of the phenomena 

 are the luminous arches, and these are therefore the best 

 adapted for determining the height ; but even these appear to 

 be by no means stationary : and as more than one are some- 

 times visible, it may, in many cases, be doubtful, whether 

 simultaneous observations, made by distant observers, refer to 

 the same arch. The Aurora of the 7th of January last made 

 its first appearance in this neighbourhood, in the south-east, 

 and in a few minutes afterwards, a single well-defined arch, 

 and which was visible but for a short time, was formed across 

 the southern meridian. If then the commencement of the 

 Aurora happened to be observed, in the form of an arch, at a 

 considerable distance to the south of the place where I observed 

 the altitude of the arch, there could be scarcely any doubt of 

 the identity of the luminous band forming these arches. It 

 appears from Mr. Harris's account of the commencement of 

 the phenomenon, that he observed an arch, at Heron Court, 

 to be elevated 55 above the northern horizon, at the same 

 time that I observed one, at Blackheath, to pass over the 

 planet Mars, then not far from the meridian, and about 46 

 above the southern horizon. Mr. Harris observed nothing to 

 the south of the zenith until some time after the first appear- 

 ance of the arch : 1 observed no arch towards the north for a 

 considerable time afterwards ; and as we observed at as nearly 



