The daily union., 1846-09-24

tion. Professor Jacobs maintains tho doctrine that
the phsno menon Of the Indian summer occurs four
times in the year, though il 10 more distinctly
marked during the autumnsl months.
NATIONAL INSTITUTE.
Read at the meeting, .dprii 4ih, 1874.
ON THE INDIAN SUMMER. BY PROFESSOR NJ
JACOBS, OF PENNsYLyANiA
1. pEyMIrios AND GENERAL cHAKAcrKR.
The season, to which, by common consent, this
term has been applied IL one Of peculiar interest TO
the peasant az well a. TO tho philosopher 70 the
community z, large as well .s to those nss wnG ais
governed.
To The former il is invested with no ordinary in
terest because il is ono Of thcse grand stages In the
annual round Of change Of season, which Is con
nected with much physical and IL may be said,
much mental enjoyment The frst winds, imme-
diately preceding the autumna equinox have swept
by, and season Of comparative quiet has sue
ceeded. The frosts have put check to vegetation,
and exposed to US the "sere and yellow leaf" The
external world has sunk into temporary repose
The air 10 calm and balmy. and the sun shines with
a mild and subdued light The hunisman goes
forth rejoicing IN his sports, the laborer Is cheerful
amid his tolls and thousand hearts are the homes
Of real pleasure.
To the latter who, equally with others, enjoy the
invigoration of body and sxhiarstion Of spirits
which it is calculated to bring with II, u comes
as xrsa fact in the world Of nature, claiming their
attention as most interesting phenomenon, inviting
their investigation, and demanding Of them the dis
coyery Of It's ply scal This cause, u 10 the
design Of the following paper, to assign The ex.
planation which will be attempted, Il is hoped VIII
not be without some appearance at least OF p'ausl-
bility. II is based, as viii throughout appear, upon
the common and well known facts Of meteoroogy.
-. .-...., ~~.,,,., M. rur oNrv oNs nm
Irs KIND occuRRNe DURING THE YEAR,
The "Indan SUMNER" is but one of class Of
similar phenomena, occurring at various times du-
ring the year. Ii 10 only moro distinctly marked
by It's greater regularity of occurrence, by the time
OF its duration, and by the dsgres Of oeseurity pro-
dueed in the sky, by its accompanying haze OF
smoke, than others of similar character Thess
are the circumstances which have forced it upon the
attention Of the community, and have exalted 1t to
such a pre-cminence, as TO make II appear ar
though il stood alone of its kind In the whole circle
of the year. But there are others, though not IN
general as well characterized AZ this, which belong
10 the same class Of phenomena, and for which the
same panaton must be given. Seasons Of compare
tive rest in the atmosphere are Of frequent occur
renee and the sky is scarcely ever free from matter
whatever that may be, which destroys Its trans
parency.
-Four periods occur, however, during the year with
considerable regularity, at which are to be witnessed
the grand distinguishing characteristics just named
The first occurs with but little variation as to
time at about the close Of October, beginning OF
November. Il is scarcely ever as late as the 18th
or 18th Of the atier-named month This is the period
Of the "Indian summer" properly so called, In It's
duration il 10 not perfectly uniform. Sometimes II
lasts two or three weeks and at others, orly few
days During the autumn Of l643, IT continued
only for FIVE days. viz: from the 18th Of October TO
the Cd Of November, and was then so family mark
ed, to have led many persons TO suppose that for
that year there was no Indian summer, and was
therefore scarcely dstinguishable from the rest Of
the season. sEs..-. -
The second occurs about the middle or close OF
April. Though not in general a. well characterized
as the period just named, il u sometimes 30 dis
tincty marked to arrest the attention of even the
casual observer. A remarkable instance Of this
kind occurred during the spring of 1888. From the
l7th or 18th Of April to the 9Th Of May, period OF
three weeks the atmosphere was subject to but lit
lle disturbances; the winds were gentle; but few
clouds were 10 "a seen; no rain fell to water the
earth; and the sby was darkened by what had the
appearance of smoke, which was afterwards en-
forced by real smoke, arising from extensive fires
then prevailing in our mountain forests. But du-
ring every year, perhaps without exception, this
peculiar state of weather may be noticed at this
period, sometimes more, and at Others less distinct
The third period occurs from about the middle of
January 10 the first week in February; and con-
sinues from five or ak days to three weeks Du-
ring this season, it not unfroquenty happens that
the farmers in Pennsylvania and Maryland, plow
the grounds designed for the reception Of their spring
crops Among the more remarkable examples Of
this kind, might be named the winters Of 1917 and
lsls and those of l842 and l643. Every year,
however, as might be expected, il not alike in this
respect Just a. is the case with the "lndian sum-
mer." .s I#fa.fff@ atNa. haa
A fourth period of similar atmospheric condition
exists during the month of August. The atmos
II. has arnk intO n afa ofa Iunoo
repose. The breezes from the south and south
west, which had almost daily, during the months Of
June and July, refreshed US, and thus rendered the
heat less oppressive, have died away. The stagnant
and sultry air has its transparency destroyed by a
thin haze or smoke, through which distant objects
appear Of whitish blue color. Thunder clouds
have diminished in frequency and extent; and hence
except during extraordinary seasons, the month Of
August is deficient in rain. The widely-extended
rain cloud does, indeed, como with its refreshing
and cheering showers, but these it distils rather
gently and quietly, and, after il has passed away,
i leaves dusky atmosphere. II is about the mid
die of the month when this state of weather mostly
occurs. ~ af
Agreeably to these views, there are, therefore,
four grand periods at which smoky or hazy atmos-
phcre pre-eminenty prevails--viz: two OF greater
intensity, occurring about month or six weeks af
ter the autumnal and vernal equinoxes, and two of
less intensity, or less distinctly Marked occurring
at about the same length of time after the summer
and winter solstices. The autumDal is of the great
est intensity, particularly so, as the immense vol
umes of actual smoke, which thrown into the air
from ten thousand fires kinded by Indians and hun
ters among the wcstern forests strewed with the re-
cently-fallen foliage, add their sombre hue to
the already existing vapor smoke The "Indian sum
mer" is therefore, only one Of these four periods,
and subject, like the rest, to vary exceedingly in
character and duration, during different years. 1t
must be regarded as only one of the annual round
of fluctuations to which the gaseous robe of earth is
subject. aa Ea. aaa
III THE CAUSES OF THESE CONDITIONS or THE AT
MosPHERE.
The principal condition Of the atmosphere during
the four periods named and from which all tho 9TH
or characteristic phenomena result, is a comparative
repose. This il found to exist either when the tenn
perature or pressure, both united have attained
a maximum or minimum, and are about to pass
to the opposite extreme.
The ordinary condition of the atmosphere is
change, arising from difference of pressure. Ofthis,
the more remote cause 10 change of temperature,
producing rarefaction or condemnation, and consc-
quently change of density. By no fair principles of
- Al