THE AURORA BOREALIS 209 



guished chemist, observed, from Kendal and Keswick, in 

 Cumberland, no fewer than 250 displays of northern 

 lights ; he established the fact that the highest part of the 

 luminous arc lies exactly above the magnetic pole, and 

 that the streamers are parallel, at least ' over a moderate 

 extent of country,' with the compass-needle as it dips 

 towards the magnetic pole, which is believed to exist in 

 the north of Canada, within the Arctic circle. 



The celebrated De la Rive, of Geneva, made an attempt 

 to reproduce the aurora in the interior of a glass vessel. 1 

 He started from the fact that the atmosphere is always 

 charged with positive electricity, and that the earth is 

 negatively electrified ; he presumed, accordingly, that the 

 two kinds of electricity would neutralise one another, and 

 that currents would, as a rule, rise vertically to the earth's 

 surface. Neutralisation occurs slowly when rain or snow 

 falls, and suddenly when lightning flashes. De la Rive's 

 theory is that in the upper regions of the atmosphere 

 electric currents circulate from the equator to the two 

 poles ; and terrestrial currents, in the interior of the earth, 

 are continually flowing from the poles towards the 

 equator. Conduction, he thought, would be easier in the 

 higher than in the lower regions of the atmosphere, and 

 also better at the poles than near the equator, because of 

 the moisture and frequent mists in the polar atmosphere. 

 The discharge through the polar air would, he believed, 

 render the mist luminous, and thus produce the pheno- 

 mena already described. 



His apparatus, which I had the good fortune to see in 

 September 1902 at Geneva, consisted of a globe with a 

 neck at each ' pole.' Through one of these necks passed 

 a copper rod A, one end of which was connected with the 

 positive discharge of an electrical machine ; at the other 

 end a ring of copper B was attached. G is an insulated 



1 Memoires de la Soc. de Phys. et d 'His. Nat. de Geneve, vol. xiii. 



O 



