No, III.] 



CAPTAIN FRANKLIN ON THE AURORA. 



551 



when it appears in an uniform stream of light, issuing from the horizon, and 

 before it has attained an altitude sufficient to give it an arched form. 



The arches of the Aurora most commonly traverse the sky, nearly at right 

 angles to the magnetic meridian, but the deviations from this direction, as has 

 been already stated, were not rare ; and I am inclined to consider, that these 

 different positions of the Aurora have considerable influence upon the direction 

 of the needle. When an arch was nearly at right angles to the magnetic meri- 

 dian, the motion of the needle was towards the west ; this westward motion was 

 still greater when one extremity of an arch bore 301°, or (about 59° to the west 

 of the magnetic north,) that is, when the extremity of the arch approached from 

 the west towards the magnetic north. A westerly motion also took place when 

 the extremity of an arch was in the true north, or about 36° to the west of the 

 magnetic north, but not in so great a degree as when its bearing was about 301°. 

 A contrary effect was produced when the same end of an arch originated to the 

 southward of the magnetic west, viz., when it bore from about 245° to 234° ; 

 and, of course, when its opposite extremity approached nearer to the magnetic 

 north. In these cases, I say, the motion of the needle was towards the east. 



In one instance only, a complete arch was formed in the magnetic meridian; 

 in another, the beam shot up from the magnetic, north to the zenith; and in 

 both these cases, the needle moved towards the west. 



The needle was most disturbed on February 13, p. m., at a time when the 

 Aurora was distinctly seen passing between a stratum of clouds and the earth, 

 or at least illuminating the face of the clouds, opposed to the observer. This 

 and several other appearances, recorded in the accompanying notes, induced 

 me to infer that the distance of the Aurora from the earth varied on different 

 nights, and produced a proportionate effect on the needle. When the light 

 shone through a dense hazy atmosphere, when there was a halo round the 

 moon, or when a small snow was falling, the disturbance was generally con- 

 siderable ; and on certain hazy cloudy nights, the needle frequently deviated 

 in a considerable degree, although the Aurora was not visible at the time. 

 Our observations do not enable us to decide whether this ought to be attributed 

 to an Aurora concealed by a cloud or haze, or entirely to the state of the atmo- 

 sphere. Similar deviations have been observed in the day-time, both in a 

 clear and cloudy state of the sky, but more frequently in the latter case. 



