ISO All Attempt to explain the Phcenomenon 



assigned seems adequate. Many of the movements, however, 

 uiay be the effect of a change from one reflecting surface to an- 

 other which presents a different angle; for sometimes there seems 

 to he a succession of different streamers, at other times only a 

 lateral motion to and fro of the same streamer. 



The illumined arch which appeared on the 24th September 

 last, and that on 1 1th September 1814, were evidently a modi- 

 fication of the aurora horealis, because they proceeded from the 

 same quarter of the heavens, and in both cases were resolved into 

 the ordinary appearance assumed by those phaenomena. These 

 facts, besides proving the latter position, go far to prove the ge- 

 neral theory here advanced. If every circumstance connected 

 with the enlightened arches is duly considered, a doubt can 

 scarcely be entertained concerning their cause. Their form, po- 

 sition, motion, and time of appearing, all concur in pointing it 

 out to be the light of the sun reflected by the spherical surface 

 of the earth, and again reflected back on a different part of it by 

 the atmosphere. From the regular form of the arches, it is pro- 

 bable that the surface from which they were reflected was that 

 of the ocean, which stretches in the direction in which the sun 

 was during their appearance. But later in the evening, when 

 that uniform surface had passed out of tlie line of direction by 

 the rotation of the earth, and the icy regions of the north j)ole 

 had intervened, the sun being reflected from a broken unequal 

 surface, the arch was also broken into streamers of the usual ap- 

 pearance. It will be obvious, that without the refractive power 

 of the atmosphere those phaenomena could have no existence, 

 because in that case the reflected rays of the sun could fall no- 

 where except in that space enlightened by his direct rays ; but 

 by refraction those rays falling upon the verge of the enlightened 

 hemisphere, must, when reflected, be bent into the dark hemi- 

 sphere. 



It is only to a certain extent within the latter boundary that 

 streamers can be seen ; for beyond that the reflected rays will 

 pass the l)ouiids when the atmosphere has power to reflect them 

 back on the earth : therefore, in our latitude, the streamers ge- 

 nerally disappear before midnight; but in higher latitudes they 

 are seen at tliut time, being nigher the boundary of light; and 

 for the same reason they are seen in the northern regions through 

 a greater part of the year, as before noticed. 



If the aurora I'orealis were of an electric or meteoric nature, as 

 is su|)posed, their height might be ascertained by the common me- 

 thod of measuring heights at any time when they are stationary; 

 but if the true origin is as above explained, the common method 

 of measuring heights will not apply to them. If they arp the re- 

 flected rays of the sun, the arch or streamer is a section of those 



rays 



