METEOROLOGY. 151

 

42° Fahr., while on the shores of California,
Oregon, and Washington, the mean is nowhere
lower than 52°, and in many places is much
higher.

In the southern portions of the eastern and

western coasts, the contrast is not so decided, —

owing to the peculiarly cool summers in the west-
ern part of the continent.

The Atlantic seaboard is much colder than corresponding
latitudes on the western coasts of Europe. For example,
the latitude of New York City is about the same as that
of Madrid, Naples, and Constantinople; of Boston, the
same as that of Rome; of Portland, Maine, the same as
that of Marseilles; of Quebec, nearly that of Paris; and
yet what a striking difference in their climates!

‘The western shores of America are, however, quite as
warm as those of Europe. Sitka, in lat. 57°, has a winter
mean very nearly the same as that of Edinburgh, in the
same latitude.

The higher mean annual temperature of the western
coasts over that of the eastern will prove of great signifi-
cance in the future history of the United States, since our
‘western shores will admit of cultivation and settlement for
amuch greater distance north than will the eastern. “The
difference,” says Blodget, “covers 12° to 15° of latitude on
the coast of the Pacific, and from 5° to 40° on the plains
east of the Rocky Mountains.

The sharp. contrast between the climate of the
eastern and western shores is caused by the at-
mospheric and oceanic circulation, which, in both
cases, is from west to east; hence, the higher tem-
perature of the western shores, on account of the
warm, vapor-laden winds from: the Pacific, the
comparatively heavy rainfall, and the warm ocean
currents. The cold Arctic current, which comes
from Baffin Bay down the Atlantic seaboard,

reduces the mean annual temperature of the.

eastern coast.

On the south, the Gulf Stream, emerging from
between Florida and Cuba, tends to raise the tem-
perature of the southern portions of the seaboard,
though its greatest influence is exerted on the dis-
tant shores of Europe. On the Pacific coast, the
Japan current, after leaving the Asiatic shores,
flows southward along the North American coasts,
bathing them with its highly heated waters.

398. Constancy of the Climate—From obser-
vations extending back as far as the year 1788, it
appears, that from that time, the climate of the
United States has undergone no decided change.

399. Distribution of Wind and Rain.—The
United States lie in the zone of the variable
winds. Westerly winds, therefore, predominate.

400. Precipitations.—The domain of the
United States is well watered, copious rains fall-
ing over nearly all portions of the surface, espe-

 

cially on those which lie east of the predominant
mountain-system.

East of the 100th meridian from Greenwich,
an average of at least 40 inches, or 33 feet, falls
throughout the year. From this large rainfall,
it is evident that the evaporation, which supplies
the winds with moisture, must take place in the
equatorial regions, and that, in general, the upper
currents of equatorial winds bring the rain. The
open sweep afforded to the winds by the Gulf of
Mexico and the Mississippi Valley, increases the
raiafall of the Gulf States.

The heaviest annual rainfall is 65 inches, and
occurs near the borders of the Gulf States, and
along the Pacific seaboard in Washington and
Oregon. Along the Atlantic border, it varies
from 40 to 45 inches; in the upper half of the
Mississippi Valley, it varies from 25 to 40 inches;
in the lower half, from 40 to 65 inches; in the
upper course of the Missouri and the region of

. the Yellowstone, from 20 to 22 inches; in por-

‘ions of the Great Basin the rainfall is very
‘limited, being but from 5 to 10 inches.

As regards its distribution in. time, rain-is pos-
sible at all seasons of the year over most of the
country ; over some portions, however, it is peri-
odical in character, these districts having a rainy
and a dry season.

East of the Mississippi River, rain may fall at
any time of the year. Near the Atlantic coast,
rain is especially abundant in the spring.

West of the Mississippi the rainfall is more
irregular. In Washington, on the Pacific coast,
rain may fall at any time during the year.
On other parts of the Pacific coast, rain is most.
frequent in winter; during the summer, it is
either scanty or wholly absent. This periodicity
in the distribution occurs mainly in the region
near the coast. In the interior, the precipitation
is more irregular.

401. The Weather Bureau—Considerable light
has been thrown on the meteorological conditions
of the United States by the operations of the
“Weather Bureau.”

The Weather Bureau was established by an
Act of Congress in February, 1870, authorizing
the Secretary of War to establish and equip
stations in different parts of the country, where
such simultaneous observations of the meteor-
ological conditions of the atmosphere could be
taken, as would enable the Department to give
timely notice to all important ports on the Atlantic