296 Prof. Olmsted on the late Periodical Visitation 



regions, where electricity is most abundant, and prevails 

 most in the polar regions, where thunder and lightning are 

 unknown. 5. That this cause is incompetent to account for 

 the auroral vapour, the material of the aurora itself. 6. 

 That the motions of the auroral vapour, in its corruscations, 

 are too rapid to be caused by electrical attractions and repul- 

 sions, but not sufficiently rapid for the electric fluid itself. 

 Finally, That electricity is inadequate to account for the 

 periodicity of the aurora, if not entirely inconsistent with the 

 secular periodicity. 



But magnetism has more claims than electricity to be con- 

 sidered as the true cause of the aurora borealis, since it is ac- 

 knowledged that the forms and positions which the streamers, 

 the arches, and the corona assume, are intimately related to 

 magnetism, and that the magnetic needle itself confirms and 

 establishes this relation. But this proves merely that the 

 matter of the aurora has magnetic properties^ but decides 

 nothing with respect to the origin of the aurora, which is the 

 principal thing to be accounted for; while magnetism, like 

 electricity, is inadequate to account for the extent, for the 

 light, for the motions, for the material, and especially for the 

 periodicity of the aurora. 



Dissatisfied with the attempts which have been made to ac- 

 count for the origin, or to explain the phenomena of the aurora, 

 from either electricity or magnetism, or from any other 

 cause of a terrestrial nature, we next look for the source to 

 the planetary spaces, and arrive at the conclusion that the 

 origin is cosmical. 



The phenomena of the aurora belong, indeed, to the atmo- 

 sphere since they are affected by the earth's diurnal rotation ; 

 but the source of the matter of which the meteor is composed, 

 w^e hold to be derived from regions above the atmosphere. This 

 distinction we deem to be of much importance in investi- 

 gating a true theory of the aurora, viz., that the exhibitions 

 are atmospheric, while the source or origin is cosmical. We 

 therefore, inquire, first, at what height in the atmosphere the 

 usual exhibitions take place ? We conclude that while some 

 of the forms of the aurora, as the corona, are unsuitable for 

 this investigation, being merely the effect of perspective, yet 



