THE AURORA BOREALIS. 267 



IV. lis atmosj)heric or terrestrial origin. 



A number of circumstances render it almost certain, not only that it 

 has a terrestrial of atmospheric origin, but that it is a phenomenon tak- 

 ing place in, and confined to the atmosphere. 



I. It does not change its position in reference to the revolving earthj 

 as do the heavenly bodies, which not being connected with it, are appa- 

 rently carried westward by its eastward revolution. But for hours to- 

 gether, it appears to occupy the same place, or to hold the same position 

 relative to the observer. It must consequently, in common with the at- 

 mosphere, have the same eastward motion with the earth. 



2. Numerous observers, whose opinions are entitled to the greatest 

 confidence, and who have had ample opportunities of forming a correct 

 estimate of its height, have agreed in assigning it, in the polar regions, a 

 place, not only far vi'ithin the limits of the atmosphere, but only a short 

 distance from the surface of the earth. 



3. The constant j)osition of the corona in the. elevated pole of the 

 dipping needle., and the near parallelism of the streamers to the direc- 

 tion of its di]} show that the aurora has a most intimate relationship to 

 terrestrial magnetism, and must have a more than casual connection with 

 the earth. 



4. It is commonly asserted by the natives and some of the temporary 

 residents in high polar regions, where the aurora displays itself on the 

 most magnificent scale, and where its rays are far more vivid than in 

 southern regions, and shoot forward with lightning velocity, that its 

 most ^active state is accompanied with a crackling or hissing sound, so dis- 

 tinct as not to be mistaken, even by those who have had no prejudices 

 or superstitious fears to lead them to believe an imaginary to be a real 

 phenomenon. "Persqns engaged in the whale fisheries," "the inhabit- 

 ants of the Shetland Islands," and those of Siberia, all agree in making 

 the same statements. But in opposition to these, are placed the state- 

 ments of some observers who, though they witnessed many polar au- 

 roras, yet never heard any sound. But this can prove no more than 

 that sound is not invariably heard. We should not expect the noise to 

 be audible except when the aurora is very low, and acting with a maxi- 

 mum intensity. Wrangell testifies that during "the most brilliant auro- 

 ras," he "did hear a slight hissing sound, as when the wind blows on a 

 flame." But in order to be heard the aurora must be within our at- 

 mosphere. 



5. It is accompanied by cloud-like matter, which has all the ordi- 

 nary external properties of true watery vapor. Wrangell says he "often 

 saw on the nortlicrn horizon, below the auroral light, dark blue clouds, 



