The daily union., 1846-09-24

temperature and certain great oscillations in the at
mosphere. In no country land ours by no means
forms exception TO the remark) docs the temper
sture pass regularly through all It's changes begin
ming with lis minimum, increasing gradually 70
maximum, and then diminishing again TO a MINI I'M
mum. Ii is only by many fluctuations 10 ana no,
but steadily advancing or reeediDg upon an ese'ase
in direction, that either maximum or MINI
mum is attained There are stages OF RAPID ehanso
for few days together, and then OF almost fepose
for the same length of time. Thus, In advancing
from the depth OF winter towards midsummer uieie
are alterations of week OF cold, and some
times blustry weather, and Of that which rs mild
and calm the latter gradually gaining upon me o,
mer; whilst, in advancing from midsummer 70 d mid
winter, similar Alterations arc followed py sfaa-
ual gain in favor Off the latter.
The barometer discloses the interesting act, that,
Independently Of those rapid variations Oh pressure
due TO the passage Of the great storm cloud thee
an intimate dependence between those alternate
stages or fluctuations just named and the average
amount of pressure. During these periods, when
the, temperature changes rapidly, though the pa
rometer Is sometimes above, apd at DINERS %
low its mean, the average is below that meani anu
during the periods Of comparative repose its aver
age is above the mean height. During the former
periods its movements are rapid, but during inc 'a'
ter they are slow. ..., n
Next to these, those oscillations in the atmos-
phere, which are dependent upon the relations OF
land and paier claim attention. To this class OF at
mospheric changes belong the land and sea breezes
and those more extensive movements which are the
result of a great body Of land surrounded by an ex-
tensive surface Of water-ofa continent bounded on
the east and west by two great oceans. These lat
ter the subject Of present consideration Even
hese fluctuations, noticed in the preceding section,
though mainly dependent upon the annual changes
Of temperature, are no doubt essentially modihed
by the relations Of our continent to its eastern and
ue The iuH of fhAae relations
demands, therefore, due attention.
1. At about the time Of the autumnal equinox,
and little afterwards, the retiring sun rapidly
| loses his power of keeping up the temperature,
which his rays had produced in the higher north
ern lattudes; contraction in the bulk, and an IN
crease in the density of that portion Of the supern-
cumbent atmosphere, and nearer approximation OF
its to the cooling earth first takes place; then
as its altitude has diminished, overhowing OF air
towards the north commences at some eleyationi
| and then Immediately, by the increased pressure,
the portion below, the earth's surface, tends
towards the place of the sun, forcing before it much
Of the air ofthe middle attitudes, and supplying its
place with that which is colder. Hence the cold
| and unpleasant winds Of October. They are the
first tribute, from the north, to the in his new
| southern home. After this first rush, by which
much of the heated air OF the north temperate zone
| has been transported southward,. an equilibrium
| gradually takes place. The land, being yet more
heated than the adjacent Atlantic ocean, keeps up
the temperature ofthe air near Its surface at point
little higher than that the ocean so that there
would be remaining tendency in the lower air to
dow towards the continent, were IL not that u Is
by the afux OF the denser air from the
higher attitudes, and by the modifying influence Of
the great circulating system, of which the "trades,
and southwestery currents are the counterparts
As however, the surface OF the land coos more rap
IDLY than that of the ocean, equality of tempera-
ture is gradually established, and the atmosphere
| becomes nearly quiescent. Gentle currents there
arc indeed arising from diarnal variations Of tenn
perature and local causes; but taking the whole
Of the atmosphere over ocean and land IN body
II is almost calm This state of quiescence, during
which the barometer stands average above Its
mean, and its movements slow, may last two OF
| three weeks, only few days. IL is the period
| Of the "Indian SUMNER" and occurs at some time
between the middle of October and the second week
| IN November. .. ..r.... ..
But in the space of from ten to twenty days, the
EARTH which is the better radiator, reduces the tenn
perature Of its surface, and that of its Immediately
superintendent air so far that by the increased den
sity of the latter aided by the horizontal pressure
/ from the north, currents are again produced. At
| these are directed mainly towards the nearest pon
! of higher temperature, they will flow towards the
warmer ocean, and nearly at right angles to its coast
Hence the production Of northwest winds at the
| breaking up of the Indian summer, and the CON-
mencement of winter. The existence of the Gull
| stream coast is no doubt prominent cause
Of the great difference of temperature land and
water on our eastern border. This current flowing
| from comparatively warm climate, and bringing
with it its warmed waters, is constantly giving ou
| to the air Immediately above it. The result being
difference Of density and PRESSURE must give rise
to winds directed from the colder land to the warmer
| gulf stream. .r....
O. A similar state Of things, only in a reverse or
der, ought to exist in spring. From the middle o
March the increasing altitude of the sun and length
Of day together produce a rapid rise of tempera.
ture in the earths surface in the northern hemis
phere. The air to a moderate height becomes heat
ed, and specifically lighter, because dated, and is
forced southwark by a greater pressure from the
north. The particular direction Of the winds is de-
termned in part by the line of our seacoast, as
already stated, and in part by the eastward tenden.
cy Of the atmosphere in our latitude.
After these March winds over, and the tenn
perature of the surface of the land and water has
been brought to an equality, an equilibrium OF
pressure must result for short time; for it is appa.
rent that the surface Of the land, which is the
better absorber, must have its temperature raised
rapidly than that of the waer and consequent.
ly there must be point Of time, a short season
when an equality in this respect must exist. This
happens about the middle or close of April some.
time after the daily absorption has become greater
than the nightly radiation. About this time, then
we must look for a season of atmospheric quies-
cence--a season of fine, pleasant weather. In gen.
eral it is not as distinctly marked, regular in its
character and long in its duration the cores
ponding autumnal season; and for these reasons, il
passes, except in peculiar cases, unnotced by
the casual observer. Ifthe more stable and perma-
nent equilibrium of autumn sometimes pass by, 80
not to arrest the attention of men, need not be
surprised find that the latter should hardly ever
be thought of as anything unusual d.
3. The similar seasons mentioned as existing
| about midwinter and midsummer or little after
are to be explained by considering them not SO much
as states of equilibrium of ofpressure between land and
water, as between the northern and southern he,nis
phres. They are in reference to temperature and
pressure what the high and low tides are to the
world of waters; the corresponding TO the time
| of minimum, and the other to the time of maximum
| temperature. .
During the rapid cooling of the northern hemis.
phere, through November, December, and January
when the daily loss of heat is greater than the gain
and the rapid heating of the southern hemisphere
in which the daily gain exceeds the loss, there is
strong determination of the lower portion of the at
mospherc to flow from the north towards the south
to displace the specifically lighter air there and o.
the upper portion to flow over from the south to-
wards the north. Thus a slow circulation between