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surface. The Isothermal bands connect themselves with the 
phenomena of animal and vegetable distribution ; and still more 
strikingly we are beginning to discover an intimate connexion 
between those regions of mean equal animal temperature and 
the great phenomena of terrestrial magnetism. The conditions 
of the ocean currents, — as, for instance, the Gulf stream 
setting northward from the Gulf of Mexico, and ameliorating 
the conditions of our own winters, — are worthy of careful study. 
The waters of the sea upon our western shores are always 
several degrees warmer than the adjoining land, and during 
last winter the ocean temperature was found to be two degrees 
higher than usual. May not the mildness of that season have 
been due to the influence of that current of water, warmed in 
inter-tropical climes, flowing northward, and yielding up its 
store of heat to the shores of these islands ? 
This ameliorating influence is strikingly shown in Norway. 
On the southern coasts of that country, which are sheltered 
from the Gulf stream by our own islands, the cereals will not 
grow ; but further northwards, where the great current setting 
to the north of Scotland reaches the Norwegian shore, the 
climate is rendered sufficiently mild for the growth of grain 
crops. 
Again, the trade winds and the monsoons are entirely 
dependent upon the operations of heat ; and careful observation 
has shown that the tornadoes of the West Indies and the 
cyclones of the Indian Seas are entirely due to the action of 
currents generated by the intensely heated surface of the earth. 
Notwithstanding the valuable researches of Sir William Reid, 
and others, proving the rotatory character of these storms, I am 
not satisfied that we have yet had a correct theory of the 
physical causes in action to produce them. 
These storms are revolving masses of air, with currents 
rushing from the circumference to the centre, and blowing up 
through that centre ; these systems of air in violent motion 
being sometimes many hundreds of miles in diameter. 
The simplest explanation appears to be, that a comparatively 
small column of air is formed by contact with the heated earth, 
which ascends with much rapidity. Take the example of a jet 
