panied by an
alteration of climate, bringing with it a set of conditions analogous
to those prevailing at certain distances further from the sun.
Ascending the Peak of Teneriffe, a series of regions are traversed,
one above another, displaying with the approach to the summit a
continually closer approximation in character to the polar regions,
till the traveller who left the palm, the cactus, and the thousand
varied forms of tropical vegetation at the foot, finds himself at last
among the stunted shrubs and scaly lichens, the borderers who hold the
outposts on the limits of the eternal snow.'

It might be expected that places on the same parallel of latitude
would be equal in temperature; but on tracing out the distribution of
heat over the globe, and laying it down in what are called
_isothermal_ lines on a map, most striking deviations are found to
exist, and the contour of the lines is anything but regular. The line
of greatest cold, for example, which leaves the eastern coast of
Labrador at about the 54th degree of latitude, rises six degrees as it
approaches Greenland, and strikes the coast of Lapland a little above
the 70th degree, or sixteen degrees nearer the pole than at its
starting-point--thus shewing that the northern parts of Europe have a
more genial climate than those of America. The line then curves
fifteen degrees to the south across Siberia, rises again on the
western coast of America, and falls once more as it advances towards
the east. Again, 'the isotherms of Canada pass through Iceland, across
about the middle of Norway and Sweden, St Petersburg and Kamtschatka.
Those of New York through the north of Ireland and England, twelve
degrees further north, North and Central Germany, and the Crimea. That
which leaves the United States at about 36 degrees north latitude,
crosses Southern Europe from the north of Spain to the Adriatic in a
tolerably straight line, some eight degrees further north, and then
falls south again, where the influence of the north-east polar current
is more felt, in Greece and Turkey.'

But although these are marked as lines of equal heat, it is only in
the average temperature that the equality consists; and it is clear
that a country with 80 degrees of summer heat and 20 of winter cold,
would have a very different climate from another with 60 and 40 as the
highest and lowest degrees of temperature, although the mean of the
two would be the same. And herein we have an explanatio