Lesson xxtv.] NORTHERS LIGHTS* 751 



did, luminous beams, well defined, and of dense 

 light; these continue i, , or 1 minute, sometimes 

 apparently at rest, but more frequently with a quick 

 lateral motion. These beams appear at all places 

 alike, to be arches of great circles of the sphere, 

 with the eye in the centre ; and these arches, it* 

 prolonged upwards, would all meet in one point. 

 This converging point is the same as that to which 

 the south pole of the dipping needle points, at the 

 place where the observation is made. Thirdly, 

 flashes pointing upward, or in the same direction 

 as the beams, which they always succeed. These arc 

 only momentary, and have no lateral motion, but 

 they are generally repeated many times in a mi- 

 nute : they appear much broader, more diffuse, and 

 of a weaker light than the beams: they become 

 gradually fainter till they disappear ; but they 

 sometimes continue for hours, flashing at inter- 

 vals. Fourthly, arches nearly in the form of rain- 

 bows. These, when complete, go quite across the 

 heavens, tending to the magnetic east and west, 

 and crossing the magnetic meridian at right angles. 



When an Aurora takes place, the appearances 

 above described generally succeed one another in 

 the following order: first, the faint, rainbow-like 

 arches; second, the beams; third, the flashes. As 

 for the horizontal light, it is found to consist of au 

 abundance of flashes or beams, blended together, 

 owing to the situation of the observer relative to 

 them. 



These phenomena have been accounted for on 



various suppositions, i. It has been supposed to 



H 4 he 



