42 ON THE RECENT SECULAR PERIOD 



exhausted tube and those of the aurora, the whole scientific world seemed to 

 acquiesce in the belief that the true cause of this phenomenon was at length disco- 

 vered; and accordingly, for a long time, a quietus was given to any further speculations 

 on the subject. 1 The discoveries recently made in the science of magnetism, have 

 led to some modification of these views ; many men of science are still tenacious 

 of the idea that electricity is the beginning and end of all that belongs to the aurora 

 borealis. 2 



Having examined some of the ablest authorities in favor of the doctrine that 

 ascribes the aurora borealis to the agency of electricity, and found that they are 

 very discordant with each other in regard to the modus operandi, and that their 

 explanations are, as appears to me, unsatisfactory, being either erroneous or defec- 

 tive, or both, I am compelled to believe that the aurora borealis does not owe its 

 origin to electricity. This opinion is strengthened by the consideration that, during 

 the prevalence of an aurora, electrometers indicate no unusual amount of atmo- 

 spheric electricity. This fact was noticed many years ago by Bergman, the Swedish 

 philosopher; and Humboldt says, recent experiments made with very sensitive 

 electrometers, have indicated no change during the finest auroras. 3 



The "currents" supposed by M, De La Rive would not, it is true, be indicated by 

 the electrometer, but only by the galvanometer. Yet it is to be remarked that 

 most of the electrical hypotheses contemplate electricity under such a form as 

 would affect the electrometer. 



Those who ascribe the aurora borealis to magnetism, seem to argue with more 

 probability, and comprise also names of high distinction in science. No one can 

 doubt that magnetism has some connection or other with the aurora, though it may 

 still be uncertain whether it be as cause or effect. The change produced in the 

 needle — the relation of the auroral columns to the magnetic meridian — the forma- 

 tion of the aurora around the pole of the dipping-needle — and the disturbance of 

 the magnetic telegraph sometimes observed during the prevalence of a great auroral 

 exhibition : these facts plainly indicate the existence of such a connection. But it 

 is to be remarked, that none of these facts touch the question of the origin of the 

 aurora, and may severally take place alike whether the origin is terrestrial or 

 cosmical. They do not account for the production of the matter of the aurora, the 

 auroral vapor; all they prove is that this vapor has magnetic properties. Even 

 Humboldt, who has been supposed particularly to favor the magnetic hypothesis, 

 since he was the first to denominate these exhibitions "magnetic storms," plainly 

 indicates in his latest publication on the subject (the third volume of Cosmos) 

 his belief in the cosmical origin of the matter of the aurora. If (says he) we 

 regard falling stars and meteoric showers as planetary asteroids, we may be 

 allowed to conjecture that in the streams of the so-called November phenomena, 



1 Sec Priestley's History of Electricity. 



3 Discussions of contested hypotheses being deemed inconsistent with the object of the Smithsonian 

 Contributions, the writer reserves his discussion of " Electrical Hypotheses of the Aurora Borealis," for 

 some other medium of publication. 



3 Cosmos, I, 186. 



