On the Height of the Aurora Borealis. 85 



that it will not only strongly support the opinion that no de- 

 pendence can he placed on observations on the altitudes of 

 aurorEe ; but that it also proves in a great degree that the 

 aurora takes place at a very little height, compared with that 

 which has generally been ascribed to it. 



It is stated in the report, that " there was very little dif- 

 ference from what appeared in London and Oxford, unless 

 that in the north of England and Scotland the light was 

 somewhat stronger and brighter." Yet this justly celebrated 

 philosopher gives the following hypothesis in explanation of 

 the various appearances reported in the many accounts of 

 this aurora, sent to the Eoyal Society. After describing the 

 perpendicular beams as caused by the rising of the magnetic 

 fluid, in columns perpendicular to the surface of the earth, 

 and the corona as caused by the beams ascending to such 

 heights " as to emerge out of the shadow of the earth, and 

 to be illustrated by the direct beams of the sun ; whence it 

 might come to pass, that the first corona was seen coloured 

 and much brighter than what appeared afterwards in some 

 places, where the sight thereof was more than once repeated, 

 after the sun was gone down much lower under the horizon ; 

 hence also it will be easily understood that the corona was 

 not one and the same in all places, but was different in every 

 differing horizon ; exactly after the same manner as the rain- 

 bow seen in the same cloud is not the same how, hut different to 

 every eye. 



In another place, he gives strong evidence of the mere local 

 appearance of auroral phenomena ; as he says, " the light had 

 now put on a form quite different from all that we have 

 hithei-to described, and had fashioned itself into the shape of 

 two lamina; or streaks, lying in a position parallel to the 

 horizon, whose edges wore but ill terminated. They extended 

 themselves from the north by east to the north-east, and 

 were each about a degree broad ; the undermost aboufeightor 

 nine degrees high, and the other aboutfour or five degrees over 

 it ; the^ekept their places for a lony time, and 7nade the sky so 

 lif/hf, that I believe a man miyht easily have read an ordinary 

 print by the help thereof Now, although these lights were 

 so different from all that had preceded them, and were so 



