628 PROFESSOR CHALLIS'S OBSERVATIONS OF THE 



streamers forming the Corona did not meet in a point, but left a circular dark space, which seemed 

 to be constant in its position, and the centre of which it was easy to fix upon. On this account I 

 consider the above results, though derived from a single observation, to be worthy of confidence. 



From a consideration of all the results derived from the foregoing discussion of observations made 

 on different occasions and at different places, the following conclusions seem to be established : — 



First, that the Corona of an Aurora Borealis is formed near the Magnetic Zenith of the place of 

 observation. 



Secondly, that the observations, while they indicate no decided difference of altitude between the 

 two points, shew with great probability that the Corona is situated between 1° and 2" more to the 

 West than the Magnetic Zenith. 



The Aurora Borealis which gave rise to the present communication, was more remarkable in its 

 features and more extensively seen than any that have occurred for a long period, having been 

 visible, as appears by authentic accounts, in France, Italy, Spain, Portugal, and the Azores. I have 

 therefore thought it would not be out of place to add here a description of it which I derived from 

 memoranda made very soon after its occurrence, and which was communicated to the Cambridge 

 Chronicle of Nov. 25, 1848. 



" Shortly after eight o'clock on the evening of Friday, Nov. 17, my attention was called to an 

 unusual appearance of light stretching from N. to W., which gave indication of a coming Aurora. 

 There was no arch, but the light was diffused and of considerable brilliancy. The maximum of the 

 brightness was at a position a few degrees N. of W., at an altitude of about 20", which appeared to be 

 a stationary centre of luminosity during the whole of the display. The diffused light increased by 

 degrees in intensity, and spread upwards till it reached the Zenith ; but during this time there were 

 no streamers. The principal features of the phienomenon were, frequent pulsations, and sudden 

 appearances and disappearances of streaks and large patches of light, so much resembling white 

 clouds that but for their rapid changes of form and brightness, it would have been difficult to dis- 

 tinguish them from the latter. The streaks darted in various quarters and different directions, 

 waning as quickly as they formed, and auroral clouds of all imaginable shapes were continually 

 bursting forth and vanishing, so as to present a spectacle of the utmost bizarrerie, till at length 

 greater order began to prevail. Streamers of some degree of definiteness arose, and in a short time 

 surrounded the magnetic Zenith. I then first observed the appearance of a corona or central point 

 towards which the streamers converged, and estimated its position at S*". 47™ Greenwich mean time, to 

 be one degree South and half a degree East of /3 Androniedie. 



" A large red patch due West and rising about 20", was observed to retain its position from s''. 35"' 

 to s''. 51™. At 8h. 56" a broad red band stretched from the Corona through Capella, and in a few 

 seconds changed to an auroral cloud of great brilliancy having Capella at its centre. At s"". 58" an 

 extraordinary red band of irregular width was formed extending across the heavens from a little S. of 

 W. to N.E. These two azimuths were the prevailing positions of the red light during the whole of 

 the phaenomenon. The band seemed to be a kind of junction of two red clouds. Its general course 

 was through a and /3 Andromedae to the Corona, and from thence its axis passed through Capella. 



" At g"". 15" the phenomenon was at its greatest height of beauty and perfection. Streamers 

 reached the Corona or Magnetic Zenith from all points of the Compass. The toiit ensemble was a 

 canopy of drapery, having the Corona for the point of divergence of the folds, and extending rather 

 more Northward than Southward of the Astronomical Zenith ; while its boundary all round was con 

 siderably elevated above the horizon. The outline was very irregular, but sharply defined, giving 

 irresistibly the idea of the lower boundary of a suspended curtain. This feature was in greatest per- 

 fection towards the N.W., where a broad space appeared so dark by contrast with the bright curtain 

 above it, that it might have been mistaken for a cloud had not stars shone through it. The predomi- 

 nating colour of the streamers was white, but about W. S. W. and N. E., the peculiar ruddy tint of 

 the Aurora was remarkably intense, and in other quarters the streamers were tinged with green and 



