SECT, xxvin.] AURORA BOREALIS. 329 



night, the scintillations of the sea reappeared ; this evening 

 the sun went down very singularly, exhibiting in its descent 

 a double sun ; and, when only a few degrees high, its sphe- 

 rical figure changed into that of a long cylinder, which 

 reached the horizon. In the night the sea became nearly 

 as luminous as before, but on the fifth night the appearance 

 entirely ceased. Captain Bonnycastle does not think it pro- 

 ceeded from animalculse, but imagines it might be some com- 

 pound of phosphorus, suddenly evolved and disposed over 

 the surface of the sea ; perhaps from the exuviae or secre- 

 tions of fish connected with the oceanic salts, muriate of soda, 

 and sulphate of magnesia. 



The aurora borealis is decidedly an electrical pheno- 

 menon, which takes place in the highest regions of the 

 atmosphere, since it is visible at the same time from places 

 very far distant from each other. It is somehow connected 

 with the magnetic poles of the earth, and occasions vibrations 

 in the magnetic needle. M. Arago has frequently remarked 

 that the needle was powerfully agitated at Paris by an 

 aurora that was below the horizon, and consequently invisible, 

 but whose existence was known from the observations of the 

 polar navigators. The aurora has never been seen so far 

 north as the pole of the earth's rotation, nor does it extend to 

 low latitudes. It generally appears in the form of a luminous 

 arch, stretching more or less from east to west, but never 

 from north to south, the most elevated point being always 

 in the magnetic meridian of the place of the observer ; and 

 across the arch the coruscations are rapid, vivid, and of various 

 colours, but whether there be any sound is still a disputed 

 point. A similar phenomenon occurs in the high latitudes 

 of the southern hemisphere. Dr. Faraday conjectures that 

 the electric equilibrium of the earth is restored by the aurora 

 conveying the electricity from the poles to the equator. 



