I ri I SCIENCE OE GARDENING. P a r t II,
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obsciTcd, tbat many situations of the moon ai*o favourable to good and others to bad
weather. , , 7 , ■ 1
1423. The sitmtims o f the moan favourable to b a i weather ma tho perigee, now and
full moon, passage of thé equator, and tho northern lunistice. Thoso belonging to tho
former are, tho apogee, quadratures, and the southern lunistice. Changes of the weather
seldom take place on tho vciy days o fth e moon’s situations, but either precede or foUow
them. I t has been found by obseiwation, that the changes affected hy the lunar
situations iu tho six winter months precede, and in the six summer months follow
them.
1424. The octants. Besides the lunar situations to winch the above observations
refer, attention must be paid also to the fonrth day before new and fiill moon, which days
are called the octants. A t these times the weather is inclined to changes; and it may
be easily seen, that these will follow at the next lunar situation. Virgil calls this fourth
day a very sure prophet. I f on that day the horns of tho moon are clear and well defined,
good weather may bo expected; but if they are duE, and not clearly mai-ked on the
edges, it is a sign that bad weather will ensue. Wlicn tho weather remains unchanged
on the fourth, fifth, and sixth days of the moon, we may conjecture that it wiU continue so
till full moon, oven sometimes till the next new moon; and in that case the lunai- situations
have only a very weak effect. Many observers of natm-e havo also remarked, that
the approach of the lunar situations is somewhat critical for tho sick. According to
Dr. Hei-sohel, tlie nearer the time of the moon’s entrance at Ml, change, or quarters, is
to midnight (that is, within two hours before and after midnight), the more fair tho
weather is in summer, but the nearer to noon the less fair. Also, the moon’s entrance at
full, change, or quarters, dmIng six of the afternoon hours, viz. from four to ten, may
be followed by fair weather; but this is mostly dependent on the wind. The same
entrance during all the hours after midnight, except the first two, is unfavom-able to faii-
weather; the hke neai-ly may be observed in winter.
1425. The artificial data are, the barometer, hygrometer, rain-gauge, and thermometer.
1426. “ B y means o f the barometer,” Taylor ohsarTOS,“w cm a enabled to regain, m some
degree at least, that foreknowledge of the weather, which the ancients unquestionably did
possess ; though we know not the data on which they founded thcir conclusions.” Chaptal
considers that the value of the barometer, as an indicator of the approaching weather, is
greater than that of the lunar knowledge of the most experienced countryman, and indeed
of all other moans put together. {La Chimie appliquée, ÿc.) ^ Wo shall thoroforo
annex such niles as Imve hitherto been found most useful in ascertaining the changes of
the weather by means of the barometer.
1427. The rising o f the mercury presages, in general, fair weather ; and its fiilling
foul weather, as rain, snow, high winds, and stoi-ms.
The sudden falling o f the mercury foretells thunder, in very hot weather, especially if
the wind is south.
The rising in winter indicates fro s t; and in frosty weather, if the mercury falls three
or four di-visions, there will follow a thaw ; but if it rises in a continued frost, snow may
be expected.
When fo u l weather happens soon after the falling ofthe mercury, it will not be of long
duration ; nor are we to expect a continuance, of fair weather, when it soon succeeds the
rising of the quicksilver.
I f, in fo u l weather, the mercury rises considerably, and continues rising for two or three
days before the foul weather is over, a continuance of fair weather may be expected to
follow.
In fa i r weather, when the mercury fa lls much ancl low, and continues falling for two
or three days before rain comes, much wet must be expected, and probably high
winds.
The unsettled motion o f the mercury indicates changeable weather.
1428. Respecting the words engraved on the register plate o f the barometer, it may bo
observed, that their exact correspondence with the state of the weather cannot be strictly
relied upon, though they wül in general agree with it as to the mercuiy rising and falling.
The engraved words are to be regarded only as indicating probable consequences of the
vaiying pressure o fth e atmosphere. The barometer, in fact, only shows the pressure of
the aerial column ; and the precipitation of rain, or the agitations of the atmosphere, arc
mei'cly events wliich experience has shoivn usually to accompany the sinking of the mercurial
column, hut are not necessarily connected with fluctuations of pressm*e. The
words deserve to be particularly noticed when the mercury removes from “ changeable”
upwards ; as those on the lower part should be adverted to, when the mercmy falls
from “ changeable” downwards. In other cases, they arc of no use : for, as its rising
in any part forebodes a tendency to fair, and its falling to foul, weather, it follows that,
though it descend in the tube from “ settled” to “ fair,” it may nevertheless be attended
B oo k II. TIIE ATMOSrnERE. 447
with a little rain, and when it rises from tho words “ much ra in ” to “ ra in ” it
shows only an inclination to become fail*, though the wet weather may still continue in
a less considerable degree than it was when the mercury began to rise. But if the
mercury, after having fallen to “ much rain,” should ascend to “ changeable,” it foretells
fair weather, though of a shorter continuance than if the mercury had risen still higher ;
and so, on the contrary, if the mercury stood at “ fair” and descends to “ changeable,”
it announces foul weather, though not of so long a continuance as if it had fallen
lower.
1429. Concavity o f the surface o f the mercury. Persons who have occasion to travel
much in the winter, and who arc doubtful whether it will rain or not, may easily
ascertain this point by the following observation :— A few hoiu*s before he commences
his iourncy, let the traveller notice the mercury in the upper part of the tube of the
barometer ; if rain is about to fah, it will be indented, or concave ; if othemisc, convex
or protuberant.
1430. Barometer in spring. Towards the end of March, or more generally in the
beginning of April, the barometer sinks vei*y low with bad weather ; after which it
seldom falls lower tlian 29 degrees 5 minutes till the latter end of September or October,
when the quicksilver falls again low with stoi-my winds, for then the winter constitution
of the air takes place. From October to April, the great falls of the barometer are from
29 degrees 5 minutes to 28 degrees 5 minutes, and sometimes lower ; whereas, during
the summer constitution of the air, the quicksilver seldom falls lower than 29 degi*ees 5
minutes. I t therefore follows that a fall of one tenth of an inch, dui*ing the summer,
is as sure an indication of rain, as a fall of between two and tliree tenths is in the
winter.
1431. The hygrometer vai*ics in material ; but cord, fiddlestring, and most of the substances
coniraonly used, become sensibly less and less accurate, so as at length not to
undergo any visible alteration from the different states of the air, in regard to dryness or
moisture. The most common of all hygrometers is that formed of the beard of the wild
oat, Avena fàtua.
1432. A sponge makes a good hygrometer on this account, as being less liable to be
changed by use than cord. To prepare the sponge, first wash it in water, and when dry,
wash it again in water wherein sal ammoniac or salt of ta rtar has been dissolved ; and
let it di*y again. Now, if the air becomes moist, the sponge will grow heavier ; and if
di-y, it will become lighter,
1433. 0*7 o f vitriol is found to grow sensibly heavier in exact proportion to the
less or greater quantity of moisture it imbibes from the air. The alteration is so great,
that it has been known to change its weight from three drachms to nine. Any deliquescent
salt, or a strong solution of a deliquescent salt such as the carbonate of potash,
commonly called oil of tartar per deliquium, may be substituted for the oil of vitriol.
1434. Steelyard hygrometer. In order to make a hygi*ometer with those bodies which
acquire or lose weight in the air, place such a substance in a scale on the end of a steelyard,
with a counterpoise which shall keep it in equilibrio in fair weather ; the other
end of the steelyard, rising or falling, and pointing to a gi*aduated index, will show the
changes.
1435. Line and plummet. I f a line be made of good well-dried whipcord, and a
plummet be fixed to the end of it, and the whole he hung <^ainst a wainscot, and a lino
be drawn under it, exactly where the plummet reaches, in vei*y moderate weather it
will be found to rise above such line, and to sink below it when the weather is likely to
become fair.
1436. The hair hygrometer o f De Saussure, and the whalebone hygrometer, originaUy
invented by De Luc, ai'C esteemed two of the most convenient now in use. In these
the quantity of moisture in the air is measured hy the amount of effect produced on
whalebone or hair.
1437. The only perfect hygrometer, however, is that of Professor Danieli, which is a
modification of that proposed by Leslie ; it depends in principle on the fact that visible
dew wiU be deposited on an artificially cooled surface at a temperature exactly proportioned
to the quantity of moisture in the air. Leslie’s consists of a siphon tube, with
a ball blown at each end (jig. 246.) and filled with ah*. A coloured
liquid fills one leg of the siphon ; the ball on the opposite limb, smoothly
coated with tissue paper, is the evaporating surface ; this is kept per-
petuaUy moist by means of a tliread passing fi*om a jai* with water as
high as the instrument to the covered ball. The cold produced by evaporation
causes the air in the baU to contract, and the colom*cd liquid
is forced into that stem by the elasticity of the air included in the naked
ball. This rise is exactly proportional to the di*yncss of the air. (T .)
1438. The rain-gauge, pluviometer, or hyetometer, is a machine for
measuring the quantity of rain that falls.