928 THAASACTIOyS OF THE AMERICAN INSTITUTE. 



occurence, in which the establishment of equilibrium between tlie 

 great tropical current and the earth should be manifested. And so 

 it would, were it not that this great current has met with many 

 interruptions, and been often arrested in its regular course by such 

 disturbances in the underlying strata, as I. have before mentioned ; 

 so nmch so, indeed, that Avlienever any portion of it is transported to 

 the polar regions, it forms rather the exception than the rule. But 

 occasionally it does, in part, reach the high latitudes, and then 

 aurora polaris can scarcely fail to appear. 



These icy needles, generated in a region of intense cold, are pecu- 

 liar. Unlike the congealation of sleet and hail, or the crystallization 

 of snow flakes from particles of water, they are precipitated directly 

 from the transparent vapor without its passing through the interme- 

 diate liquid state. Like the ultimate vesicles and other individualities 

 of a cloud, they maintain their own independent electrical spheres, 

 and not only repel each other, but are, from their very inception, 

 polarized. 



The molecules of the vapor, too, of which they are formed, I 

 infer, were polarized, and were, therefore, forced to unite in the exact 

 manner to give them their peculiar filamentous or needle like form. 

 Being precipitated from vapor, intensely positive, they themselves 

 are endoM^ed with positive electricity equally intense. 



How then must they dispose themselves, in their relation to each 

 other, when floating freely in the air? Certainly in parallelism, and 

 with their positive poles directed toward the negative earth ; there- 

 fore, wlien discharges between such haze and the earth, or the lower 

 stratum of moist air become visible, they must appear in lines parallel 

 with the direction of the icy needles. How beautifully apparent, 

 then, is the rationale of those splendid displays; the flickerings, the 

 streamers, the corona and the merry dances, all moving in exact 

 obedience to the slightest electric or atmospheric changes. But 



Tereestkial Magnetism 

 has an effect, in a M-ay, not yet well understood, in modifying and 

 giving direction to the auroral movements. The well known effect 

 of a magnet upon the electric arch between the poles of a powerful 

 battery, and upon discharges through rarified air, are supposed to 

 present some analogy to this terrestrial magnetic effect. 



We are now obliged to discard the idea of extra atmospheric 

 aurora, as well as that of reflected solar light, and nnist adniit that 



