The Sun.
London, England, 1860-09-12 00:00:00

oB' TO FORETELL WEATHER.

"fhe for lowing manual of the barometer has been
socoPilei d by Rear-Admiral Fitzroy, and published
by the Board of Trade
.amiliar as the practical use of weather-glasses
is, at . sea as well as on land, only those who have
e watched their indications and compared them
refully are really able to conclude more than that
Vie rising glass a usually foretells less wind or rain,
Ss falling barometer more rain or wind, or both ; a
high one fine weather, and a low the contrary.
But, useful as these general conclusions are in
most cases, they are sometimes erroneous, and then
remarks may be rather hastily made, tending to
discourage the inexperienced.
" By attention to the following observation (the
results of many years' practice and many persons'
experience) any one accustomed to use a barometer
may do so without difficulty.
" The barometer shows whether the air is get-
ting lighter or heavier, or is remaining in the same
state. The quicksilver falls as the air becomes
lighter, rises as it becomes heavier, and remains at
rest in the glass tube while the air is unchanged in
weight. Air presses en everything within about 40
miles of the world's surface like a much lighter
ocean, at the bottom of which we live, not feeling
its weight because our bodies are full of air,b but
feeling its currents, the winds. Towards any place
from which the air has been drawn by suction e air
presses with a force or weight of nearly 151 b. on
a square inch of surface. Such a pressure holds
the limpet to the rock when, by contracting itself,
the fish :has made a place without air d under its
shell. Another familiar instance is that of the fly,
which walks on the ceiling with feet that stick.
The barometer tube, emptied of air, and filled with
pure mercury, is turned down into a cup or cistern
containing the same fluid, which, feeling the weight
of air, is so pressed by it as to balance a column of
about 30 inches (more or less) in the tube, where no
air presses on the top of the column.
" If a long pipe, closed at one end only, were
emptied of air, filled with water, the open end kept
is water and the pipe held upright, the water
would rise in it more than 30 feet. In this way
water barometers have been made. A proof of this
effect is shown by any well with a sucking pump,
up which, as is commonly known, the water will
rise nearly 30 feet by what is called suction, which
is, in fact, the pressure of air towards an empty
place.
" The words on scales of barometers should not
be so much regarded for weather indications as the
rising or falling of the mercury, for if it stand at
changeable' and then rise towards fair' it pre-
sages a change of wind or weather, though not so
great as if the mercury had risen higher • and, on
the contrary, if the mercury stand above' 'fair' and
then fall it presages a change, though not to so
great a degree as if it had stood lower; besides
which, the direction and force of wind are not in
any way noticed. It is not from the point at which
the mercury may stand that we are alone to form
a judgment of the state of the weather, but from
its rising or falling, and from the movements of im-
mediately preceding days as well as hours, keeping
in mind effects of change of direction and dryness
or moisture, as well as alteration of force or strength
of wind.
"In this part of the world, towards the higher
latitudes, the quicksilver ranges, or rises and falls,
nearly three inches—namely, between about 30
inches and 9-tenths (30.9) and less than 28 inches
(28.0) on extraordinary occasions ; but the usual
range is from about 30 inches and a half (30.5) to
about 29 inches. Near the Line, or in equatorial
places, the range is but a few tenths, except in
storms, when it sometimes falls to 27 inches.
" The sliding-scale (vernier) divides the tenths
into 10 parts each, or hundredths of an inch. The
number of divisions on the vernier exceeds that in
an equal space of the fixed scale by one.
"By a thermometer the weight of air is not
shown. No air is within the tube. None can get
in. But the bulb of the tube is full of mercury,
which contracts by cold and swells by heat, accord-
ing to which effect the thread of metal in the small
tube is drawn down or pushed up so many degrees,
and thus shows the temperature.e
" If a thermometer have a piece of linen round
the bulb, wetted enough to keep it damp by a
thread or wick dipping into a cup of water, it will
show less heat than a dry one, in proportion to the
dryness of the air and quickness of drying. I In
very damp weather, with or before rain, fog, or
dew, two such thermometers will be nearly alike.
" For ascertaining the dryness or moisture of
air, the readiest and surest method is the compari-
son of two thermometers, one dry, the other just
moistened and kept so. Cooled by evaporation as
much as the state of the air admits, the moist (or
wet) bulb thermometer shows a temperature nearly
equal to that of the other one when the atmosphere
is extremely damp or moist ; but lower at other
times, in proportion to the dryness of air and con-
sequent evaporation—as far as 12 or 15 degrees in
this climate, 20 or even more elsewhere. From 4 to
3 degrees of difference is usual in England, and
about 7 is considered healthy for inhabited rooms.
" The thermometer fixed to a barometer intended
to be used only as a weather-glass shows the tem-
perature of air about it nearly, but does not show
the temperature of mercury within exactly. It
does so, however, near enough for ordinary practi-
cal purposes, provided that no sun, nor fire, nor lamp
heat is allowed to act on the instrument partially.
" The mercury in the cistern and tube being
affected by cold or heat, makes it advisable to con-
sider this when endeavouring to foretell coming
weather by the length of the column.
" Briefly, the barometer shows weight or pres-
sure of the air ; the thermometer, heat and cold, or
temperature ; and the wet thermometer, compared
-with a dry one, the degree of moisture or damp-
ness.g
" It should always be remembered that the state
of the air foretells coming weather, rather than
shows the weather that is present—an invaluable
fact too often overlooked ; that the longer the time
between the signs and the change foretold by them,
the longer such altered weather will last; and, on
the contrary, the less time between a warning and
a change, the shorter will be the continuance of
such foretold weather.
" To know the state of the air, not only barome-
ter and thermometer should be watched, but the
appearances of the sky should be vigilastly noticed.
"If the barometer has been about its ordinary
height, say near 30 inches (at sea level).h and is
steady, or rising, while the thermometer falls, and
dampness becomes less, north-westerly, northerly,
or north-easterly wind, or less wind, less rain or
snow may be expected.
" On the contrary, if a fall takes place with a
rising thermometer and increased dampness, wind
and rain may be expected from the south-eastward,
southward, or south- west ward.
" A fall with a low thermometer foretells snow,
" Exceptions to these rules occur when a north-
easterly wind, with wet (rain, hail, or snow) is
impending, before which the barometer often rises
(on account of the direction of the coming wind
alone) and deceives persons who, from that sign
only (the rising) expert fair weather.
" When the barometer is rather below its ordi-
nary height, say down to near 29;1,- inches (at the
sea level), a rise foretells less wind, or a change in
its direction towards the northward, or less wet;
but when it has been very low, about 29 inches, the
first rising usually precedes or indicates strong
wind ; at times heavy squalls from the north-west-
ward, northward, or north-eastward,—after which
violence a gradually rising glass foretells improving
weather if the thermometer falls; but, if the
warmth continue, probably the wind will back
(shift against the sun's course), and more southerly,
or south-westerly wind will follow, especially if the
barometer rise is sudden.
"The most dangerous shifts of wind, or the
heaviest northerly gales, happen soon after the
barometer first rises from a very low point ; or, if
the wind veers gradually, at some time afterwards.
" Indication of approaching changes of weather
arid the direction and force of winds are shown less
by the height of the barometer than by its falling
or rising. Nevertheless, a height of more than
thirty (30 0) inches (at the level of the sea) is indi-
cative of fine weather and moderate winds; except
from east to north, occasionally.
" The barometer is said to be falling when the
mercury in the tube is sinking, at which time its
upper surface is sometimes concave or hollow; or
when the hand (see note in page 2) moves to the
left. The barometer is rising when the mercurial
column is lengthening ; its upper surface being
convex or rounded, or when the hand moves to the
right (see note in page 2).
„ A rapid rise of the barometer indicates unsettled
weather ; a slow movement the contrary ; as like-
wise a steady barometer, which, when continued,
and with dryness, foretells very tine weather.
I,eather
and consid
or snowerable fail
is a sign of stormy
( ) .
" A r
Alternate rising and
anapidd rata
sinking indicates unsettled and threatening weather.
The greatest depressions of the barometer are

cksi
" a Glue, barometer, column, mercury, qui lver, or
band. atmospheric fluid which We
" b Or atmosphere, or the tit
breathe.
" c Or exhaustion.
" d A vacuum.
e Thirty-two degrees is the point at which water begins
to freeze or ice to thaw.
" f Evaporation.
g The two thus combined making a hygrometer ; for
which some kinds of hairshift.
, grass, or seaweed may be a make-
"h It differs, or stands lower, about a tenth of an inch
for each hundred feet of height directly upwards, or verti-
cally, above theiseaci,lt,
average height being 29.94 inches
Alt the mean, sea
r level t,___nlitland. Allowances must, there. 1
0/*) Da "e for wir°Dl4"ll% land or in buildings. A

with gales from S.E., S., or S.W. t • the greatest
elevations, with wind from N.V., N., or N.E., or
with calm.
" Though the barometer generally fal's with a
southerly and rises with a northerly win I, the con-
trary sometimes occurs ; in which cases, the
southerly wind is usually dry with fine weather,
or the northerly wind is violent and ccompanied
by rain, snow, or hail ; perhaps with ightning.
"When the barometer sinks considerably, much
wind, rain (perhaps with hail), or snow will fol-
low ; with or without lightning. The wind will be
from the northward, if the thermometer is low (for
the season)—from the southward, if the thermome-
ter is high. Occasionally a low glass is followed or
attended by lightning only, while a storm is beyond
the horizon.
" A sudden fall of the barometer, with a westerly
wind, is sometimes followed by a violent storm
from N.W. or N. or N.E.
" If a gale sets in from E. or S.E., and the wind
veers by the S. the barometer will continue falling
until the wind is near a marked change, when a
lull may occur ; after which the gale will soon be
renewed, perhaps suddenly and violently, and the
veering of the wind towards the N.W., N., or N.E.
will be indicated by a rising of the barometer with
a fall of the thermometer.
" Three causes (at least)a appear to effect a baro-
meter :
~ 1. The direction of the wind—the north-east
wind tending to raise it most—the south-west to
lower it the most, and wind from points of the com-
pass between them proportionally as they are nearer
one or the other extreme point.
"N.E. and S.W. may therefore be called the
wind's extreme bearings (rather than poles).
" The range or difference of height shown, due to
change of direction only, from one of these bearings
to the other (supposing strength or force, and mois-
ture to remain the same), amounts in these latitudes
to about half an inch (as read off).
" 2. The amount—taken by itself—of vapour,
moisture, wet, rain, or snow in the wind, or current
of air (direction and strength of wind remaining the
same), seems to cause a change amounting in an
extreme case to about half an inch.
" 3. The strength or force alone of wind, from
any quarter (moisture and direction being un-
changed), is preceded or foretold by a fall or rise,
according as the strength will be greater or less,
ranging in an extreme case to more than 2 inches.
" Hence, supposing three causes to act together
—in extreme cases—the height would vary from
near 31 in. (30.9) to about 27 in. (27.0), which has
happened, though rarely (and even in tropical lati-
tudes).
"In general, the three causes act much less
strongly, and are less in accord ; so that ordinary
varieties of weather occur much more frequently
than extreme changes.
"Another general rule requires attention ; which
is, that the wind usually appears to veer, shift, or
go round with the sun (right-handed, or from left
to right),b and that when it does not do so, or backs,
more wind or bad weather may be expected instead
of improvement.
" It is not by any means intended to discourage
attention to what is usually called `weather wis-
dom.' On the contrary, every prudent person will
combine observation of the elements with such in-
dications as he may obtain from instruments; and
will find that the more accurately the two sources
of foreknowledge are compared and combined, the
more satisfactory their results will prove.
" A barometer begins to rise considerably before
the conclusion of a gale, sometimes even at its com-
mencement. Although it falls lowest before high
winds, it frequently sinks very much before heavy
rain. The barometer falls, but not always, on the
approach of thunder and lightning.c Before and
during the earlier part of settled weather it usually
stands high and is stationary, the air being dry.
" Instances of fine weather, with a low glass, oc-
cur, however rarely, but they are always preludes
to a duration of wind or rain, if not both.
" After very warm and calm weather, a storm or
squall, with rain, may follow ; likewise at any time
when the atmosphere is heated much above the
usual temperature of the season.
" Allowances should invariably be made for the
previous state of the glasses during some days, as
well as some hours, because their indications may
be affected by distant causes, or by changes close at
hand. Some of these changes may occur at a greater
or less distance, influencing neighbouring regions,
but not visible to each observer whose barometer
feels their effect.
" There may be heavy rains or violent winds be-
yond the horizon, and the view of an observer, by
which his instruments may be affected considerably,
though no particular change of weather occurs in
his immediate locality.
" It may be repeated that the longer a change of
wind or weather is foretold before it takes place,
the longer the presaged weather will last, and con-
versely,the shorter the warning the less time, what-
ever causes the warning, whether wind or a fall of
rain or snow, will continue.
" Sometimes severe weather from the southward,
not lasting long, may cause no great fall, because
followed by a duration of wind from the northward,
and at times the barometer may fall with northerly
winds and fine weather, apparently against these
rules, because a continuance of southerly wind is
about to follow. By such changes as these one may
be misled, and calamity may be the consequence, if
not duly forwarned.
"A few of the mere marked signs of weather,
useful alike to seaman, farmer, and gardener, are
the following :
" Nether clear or cloudy, a rosy sky at sunset
presages fine weather; a rel sky in the morning
bad weather or much wind, perhaps rain ; a gray
sky in the ramming, fine weather; a high dawn,
wind ; a low dawn, fair weather.cl
" Soft-looking or delicate clouds foretell fine wea-
ther, with moderate or light breezes; hard edged,
oily-looking clouds, wind. A dark, gloomy, blue
sky is windy, but a light, bright blue sky indicates
fine weather. Generally the softer clouds look the
i less wind (but perhaps more rain) may be expected;
and the harder, more ' greasy,' rolled, tufted, or
ragged, the stronger the coming wind will prove.
Also, a bright yellow sky at sunset presages wind ;
a pale yellow, wet ; and thus by the prevalence of
red, yellow, or gray tints, the coming weather may
be foretold very nearly; indeed, if aided by instru-
ments, almost exactly.
" Small inky•looking clouds foretell rain ; light
scud clouds driving across heavy masses show wind
and rain, but if alone may indicate wind only.
" High upper clouds crossing the sun, moon, or
stars in a direction different from that of the lower
clouds, or the wind then felt below, foretell a
change of wind e ■
" After fine clear weather, the first signs in the
sky of a coming change ure usually light streaks,
curls, wisps, or mottled patches of white distant
cloud, which increase, and are followed by an over-
casting of murky vapour that grows into cloudiness.
This appearance, more or less oily, or watery, as
wind or rain will prevail, is an infallible sign.
" Usually the higher and more distant such clouds
seem to be—the more gradual, but general, the corn-
ing change of weather will prove.
" Light, delicate, quiet tints or colours, with soft,
undefined forms of clouds, indicate and accompany
fine weather, but gaudy or unusual hues, with hard,
definitely outlined clouds foretell rain, and probably
strong -wind.
1 " Misty clouds forming, or hanging on heights,
1 show wind and rain coming—if they remain, in-
crease or descend,
flyloforutbtheeecayormiryie-,se or disperse the
seaill improve birds
weather,,tien w
and far to seaward,
moderate wind and fair weather may be expected ;
when they hang about the land, or over it, some-
times flying inland, expect a strong wind with
stormy weather. As many creatures besides birds
are affected by the approach of rain or wind, such
indications should not be slighted by an observer
who wishes to foresee weather.
" There are other signs of a coming change in the
weather known less generally than may be desirable,
and therefore worth notice ; such as when birds of
hleonmge,and
flight, rooks, swallows, or others, hang about
fly up and down or low—rain or wind
may be expected. Also when animals seek sheltered
places, instead of spreading over their usual range;
when pigs carry straw to their sties ; when smoke
from chimneys does not ascend readily (or straight
upwards during calm), an unfavourable change is
probable.

" Dew is an indication of fine weather ; so is fog.
Neither of these two formations occurs under an
overcast sky, or when there is much wind. One
sees fog occasionally rolled away, as it were, by
wind—but seldom or never formed while it is
blowing.
" Remarkable clearness of atmosphere near the
horizon, distant objects, such as hills, unusually
visible,or raised (by refraction)f and what is called
' a good hearing day,' may b• mentioned among the
signs of wet, if not wind, to be expected.
" More than usual twinkling of the stars, indis-
tinctness or apparent multiplication of the /noon's

" a Electrical effects are yet uncertain.
" With watch hands in the northern hemisphere; but
the contra in south latude. This, howevr, is only ap-
parent ; the wind is actually circulating ine the contrary
direction.
" c Thunder clouds rising from north eastward against
the wind do not usually cause a fall of the barometer.
A high dawn' is when the first indications of day-
light are seen above a bank of clouds. A low dawn' is
When the day breaks on or near the hor;son, the first streaks
of light being lo do.
" e In the t veryropics, or regions of trade winds, there is ge-
nerally an upper and
counter current of air, with very light
clouds, which is not an indication of any approaching
change. In middle latitudes such upper currents are not
so frequent (or evident ?) except before a ohange of
fNucla refraction is sign of easterly rind. weather,