OF TUE AURORA BOREALIS. 45 



longitude come up to this point, one after another, they would receive their 

 respective portions of the auroral matter at times corresponding to the diurnal 

 revolution, and have their exhibition everywhere at the same hour of local time, 

 for the same reason that it is now everywhere noon to places coming successively 

 under the meridian. 1 



Thirdly, we urge the cosmical origin of the aurora borealis, from the considera- 

 tion that the velocity of the motions is too great for any terrestrial matter. These 

 motions (as, for example, that of the streamers rushing up to the pole of the 

 dipping needle to form the corona) cannot be considered as the progress of light 

 itself, or of electricity, or of magnetism, since the apparent motion of each of these 

 agents is instantaneous, while this is progressive; nor can they be ascribed to 

 electric or magnetic attractions and repulsions, because they are too rapid to 

 be produced by them, since auroral vapor, estimated at the height of 70 or 100 

 miles above the earth, is translated from the horizon to the zenith in a few seconds, 

 and auroral waves dart over 90° in a single second. Where do we meet with 

 matter moved by any terrestrial force that is subject to a velocity like this ? If 

 indeed the motions of what are called auroral waves are undulatory and not 

 progressive, their appearance is wholly unearthly, and unlike to any other undula- 

 tions with which we are acquainted. But portions of a nebula, under or through 

 which the earth passes, may easily be conoeived to have any velocity relative to 

 the earth, within the limits exhibited by the auroral matter. This matter is 

 present; it has motions too rapid to be produced by any terrestrial forces; we 

 infer, therefore, that it has come to us from a region extrinsic to the earth, endued 

 with a velocity known to exist among bodies, whether solid or nebulous, that 

 revolve around the sun. 



Fourthly, we infer the cosmical origin of the aurora borealis from its periodicity, 

 especially its secular periodicity. "Whether we have succeeded or not in establish- 

 ing a definite interval of 65 years, from the beginning of one of these auroral 

 visitations to the beginning of another, the general fact cannot be doubted of the 

 occurrence of great periods when, during 20 years or more, these exhibitions return 

 in greatly increased splendor and frecmency, and then, for many years, are scarcely 

 seen except in their humbler forms. Now the terrestrial forces assigned, as elec- 

 tricity and magnetism, are not subject to any such periodicity, but are in a state 

 of constant activity. The most delicate instruments indicate no corresponding long 

 periods of activity and repose in these agents. On the contrary, a nebulous body 

 revolving around the sun, may readily be conceived to have its periods so nearly 

 commensurable with those of the earth that the two bodies shall remain for a long 



1 Captain Lefroy, an able and assiduous inquirer into the laws of the aurora borealis, has remarked 

 this fact, although he probably would not agree with us in respect to the cause assigned. He says : 

 " It is remarkable that, in many cases, the phenomenon was first seen, in absolute time, at the north- 

 eastern stations, notwithstanding the earlier commencement of darkness at the extreme north, where the 

 difference of latitude in some cases more than compensates for the difference of longitude. It would 

 appear from this, that the aurora does not commonly appear at a station on any meridian until that 

 meridian generally is in darkness ; a result which, if established by the whole body of evidence, will be 

 both new and interesting." — Second Report, 1850-1. 



