OF THE AURORA BOREALIS. 43 



when, as in 1799, 1833, and 1834, myriads of falling stars traverser! the vault of 

 heaven, and northern lights were simultaneously observed, our atmosphere may 

 have received from the regions of space some elements foreign to it, which were capable 

 of exciting electro-magnetic processes} If magnetism is inadequate to account for 

 the origin of the aurora and for the production of the material of which it is com- 

 posed, no more adequate is it to account for the phenomena that attend it, such as 

 the extent, the light, the motions and the periodicity. 



After having carefully examined the leading hypotheses which have been 

 advanced to explain the cause of the aurora borealis, they all appear to me to be 

 inadequate and unsatisfactory. It is required of a theory that it be a deduction 

 from well-established truths; and of an hypothesis, that it explain the leading facts, 

 and that it be not inconsistent Avith any known facts, although its application in 

 certain cases may not be readily perceived. An explanation which unites the 

 characters of both, which is at once an inference from acknowledged truths, and 

 which affords an adequate solution of the leading phenomena, is deemed peculiarly 

 worthy of confidence until a better can be proposed. Such is the explanation which, 

 in conclusion, I shall attempt. 



The origin of the Aurora Borealis is cosmical, the matter of which it is composed 

 being derived from the planetary spaces? First, I argue the cosmical origin of 

 the material of these exhibitions from their great extent. That of November 

 17, 1848, was seen under nearly the same appearances, at Smyrna and Odessa, 

 and on the western coast of Asia, in England and Scotland, in Cuba, and 

 throughout the United States as far west as San Francisco, 3 extending over at 

 least 153° of longitude and 40° of latitude, and we know not how much further. 

 Does it seem probable that such an amount of auroral vapor could have been 

 all at once emitted from the earth, or have been precipitated from the atmosphere, 

 like the particles of ice and snow supposed by M. De La Rive, for example ; or 

 that the electric or magnetic equilibrium should, in an instant, or within a few 

 hours, have been disturbed over so large a portion of the earth's surface? And 

 if the causes supposed could give such an amplitude to the aurora, are any known 

 exhalations from the earth, or precipitations from the atmosphere, ever found to 

 reach so high as the elevation to which the auroral matter sometimes, if not 

 always, attains — a height at least 100 miles above the earth ? The very extent of 



1 Cosmos, III, 41. 



2 My opinion of the cosmical origin of the aurora, was expressed in my lectures to the students of 

 Yale College, as early as 1835, and soon afterwards at a meeting of the Connecticut Academy. In my 

 account of the great aurora of January 25, 1837, in the American Journal of Science, Vol. XXXII, 

 p. 180, the following language is used : "Nor can I add, at present, anything respecting the origin of 

 the aurora borealis, except to declare my conviction that it is not satisfactorily accounted for by any 

 existing theory. In assigning it so hastily to electricity, a quietus was given to all further attempts at 

 explanation, while yet even the presence of this agent, in any extraordinary degree, has never been 

 proved. Magnetism has done more ; the auroral vapor is proved to have magnetic properties ; but stifl 

 this fact gives us no information respecting its origin. This, I believe, is to be sought for in a source 

 extrinsic to the earth." 



3 Amer. Jour, of Science, N. S., VII, pp. 121, 293. 



