238 Causes of the Aurora Borealis. 



One writer presumes that the electrical fluid is attracted and accu- 

 mulated by the immense masses of iron, which is a native product ol 

 those regions from 32° north lat. to the pole,* Professor Hansteen . 

 attempts to account for it by considering it an electro-magnetical 

 phenomenon, but after advancing an extremely elaborate hypothesis 

 upon the influences of " neutralized electricity" which he supposes 

 identical with magnetism, he remarks, " I confess that there still re- 

 main various obscurities in this difficult subject, not easily to be solv- 

 ed."! A late writer in *e London Phil. Mag. attributes it to the 

 reflection of the solar light from the polar ices, refracted by the 

 power of the atmosphere into the upper regions of the air, and again 

 refracted so as to be made visible within certain limits, to the inhab- 

 itants of the earth. 



Those theories which attribute this phenomenon to electricity, are 



met by the following unanswerable objections. The electric fluid 



never accumulates in visible cohesive masses ; it is always dispersed 



through the earth and air, and its tendency is to remain in eqtnhbno 



or nearly so, unless when collected by some medium different from 



the atmosphere, as in thunder clouds ; its velocity, when moving, is 



greater perhaps than that of any other substance, not excepting even 



light itself, and when it becomes luminous, it is more fugitive than 



under any other form. The electric fluid never undulates, or waves 



to and fro in sinuous curves and motions, nor does it settle in banks 



of steady light, or remain at once luminous and stationary, m any 



form, in the pure air. Thus it is plain that if the metallic regions 



were capable of attracting the electric effluvia and suspending them 



between the heavens and the earth, still there must be some other 



medium than the pure air to detain and make them luminous. 



the medium, and the effect were both produced by that cause, the 



effect should be constant, for the action of the attracting force is ever 



in operation, and not occasional and evanescent as the clouds which 



attract and conduct the liehtninc;. 



The magnetic efflux is not only not inherently luminous, but in- 

 capable of reflecting light. 



The supposition of Becearia, that the electric fluid in seekin 

 south pole became visible in its passage from the north, is negative 

 by the fact, that the aurora appears in the southern temperate zone. 



* Am. Jour. Science, Vol. xvi, p. 291. t lb. Vol. xiv ? p. 110 



