SECT. XXVIII. AURORA BOREALIS. 289 



slowly, and the sun rose of a fiery and threatening as- 

 pect. Rain followed. Captain Bonnycastle caused a 

 bucket of this fiery water to be drawn up ; it was one 

 mass of light when stirred by the hand, and not in sparks 

 as usual, but in actual coruscations. A portion of the 

 water preserved its luminosity for seven nights. On 

 the third night, .the scintillations of the sea reappeared ; 

 this evening the sun went down very singularly, exhibit- 

 ing in its descent a double sun ; and when only a few 

 degrees high, its spherical 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. Cap- 

 tain Bonnycastle does not think it proceeded from ani- 

 malculae, but imagines it might be some compound of 

 phosphorus, suddenly evolved and disposed over the sur- 

 face of the sea ; perhaps from the exuviae or secretions 

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



a-,nd sulphate of magnesia. 



The aurora borealis is decidedly an electrical phenom- 

 enon, 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 oc- 

 casions 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 hori- 

 zon, 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 colors, 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. 



19 BB 



