40 
A VOYAGE TO SPITZBEBGEN. 
probably on or near the same parallel of latitude. 
In 1663 it was due north of Paris : it then advanced 
westwardly till about 1819, when it returned east- 
wardly, in which direction it is still moving, and 
Bond supposes that the eastern limit will be reached 
in about 2140. There are so many resemblances and 
analogies between the secular and local distribution 
of the"elements of terrestrial magnetism and heat that 
many persons are convinced that there is an intimate 
connection between them. The magnetic Pole lies 
near the region of greatest mean cold, and its course 
appears to be along the zone of lowest mean tempe¬ 
rature. Auroras are believed to be essentially the 
results of magnetic disturbance, and originate, or at 
any rate are most abundant and energetic along a 
zone situated on and near the latitude of the magnetic 
Pole, which is probably that of greatest cold. It is 
inferred that no auroras are produced north of about 
80°; in other words, that a person at the Pole would 
see the auroras on the southern sky. The alternate 
heating and cooling of the Polar area, together with 
the great difference of temperature between the zone 
of greatest cold and the tropic of the northern hemi¬ 
sphere, would seem an adequate and probable cause 
for the generation of magnetic currents and storms. 
The auroras are observed to occur in cycles of varying 
