116 AURORA BOREALIS. 



intervene, either above or below the point of incidence, the pheno- 

 menon will disappear. 



When the rays of the sun are reflected from a vast plain of icy 

 substance to stationary and to us invisible clouds, it follows that the 

 Aurora will remain a long time without changing, the rays being 

 then reflected as from a circular or globular mirror, the angle of 

 incidence and reflection remaining the same ; but the moment that 

 these rays arrive (by the earth's rotation) at water, or at some non- 

 reflecting substance or surface, the Aurora suddenly disappears, as 

 it does by an intervening cloud, which is a fact I have had con- 

 firmed by many observations. 



With regard to the action of the Aurora on the magnetic needle, 

 I need only say, that in common with every other kind of light, it 

 has the property of affecting the needle or combining with mag- 

 netism. The effects of tlie Aurora on the needle were the same as 

 the sudden approach of a naked candle, or when the light of 

 a lamp was concentrated by a lens on the needle delicately 

 suspended at a distance of eighty-four yards : an experiment which 

 I repeatedly tried at Sheriff"*s harbour. With regard to electricity, 

 it is notorious that there is less in the Arctic Regions than in any 

 other place; and, during my first voyage, the electrometer was 

 never moved by the electric fluid, although often tried. 



The position of the Aurora Borealis in the heavens, depends 

 much on the depression of the sun below the liorizon of the spec- 

 tator, on its bearings, and on the nature of the surface which first 

 receives the sun's rays, at the point of incidence, which if uneven 

 will produce the capra saltans^ or merry dancers; if the surface is 



