ual
temperature, starting from the vicinity of Boston and running west, which
showed most remarkably the rise of the summer lines as intensity
increased, and the fall of the winter lines in like manner.

The influence of the lakes was also most obvious. The elevation of the
earth increases, going west, to about 700 feet at the surface of the
lakes, and to nearly 4,000 feet at the eastern base of the Rocky
Mountains; and, although temperature does not decrease to as great a
degree when the elevation above the level of the sea is _gradual_, yet
some allowance should doubtless be made for that elevation on this line.
When that allowance is made, the ascent of the summer line, to the north,
over the area of greatest intensity, is strikingly apparent.

Dr. Forrey also instituted a comparison between Fort Snelling, where the
climate is as excessive, and the range of the thermometer as great, as in
any portion of the continent in the same latitude, with Key West, and I
copy his diagram. It is very instructive, showing the gradual mean rise of
the temperature, from January to December, inclusive, while the cross
lines show the _extremes of each month_.

Perhaps the most interesting part of it, is the illustration of the
monthly extremes, and the contrast between them, in the excessive climate
of Fort Snelling, and the tropical one of Key West. Each is a type of the
climate in which it is situated. The annual range and monthly extremes are
small in tropical countries, and large in extra-tropical ones. The extreme
range, or greatest elevation of heat, contrary to what is generally
supposed, is greater at Fort Snelling than at Key West. But the climate of
the latter is modified by the adjoining ocean.

I copy, also, a table (p. 304), showing the range of the thermometer for
the year, and the maxima and minima, during each month, at several other
places in this country, and at London and Rome, for the purpose of showing
the extent of the ranges compared with those places; and also, that these
great changes in each month occur very uniformly all over the country,
and may always be expected, and with considerable regularity. They are
incident to our climate. I wish I could engrave the foregoing diagram, and
the following table, upon the mind of every man, woman, and child in the
country; and under it, in ever-visible letters, these words of precaution:
CONFORM TO THE PECULIARITIES OF YOUR CLIMATE, AND CLOTHE YOURSELVES, AT
ALL TIM