II
1439. A holbm cylinder fomis ouo of tlio best coustmcted rain-gaugos; it
has within it a cork ball attached to a wooden stem ( f y . 247.), which passes
through a smidi opening at tho top, on which is placed a large funnel. When
this instniment is placed in the open air in a free place, the rain that falls
within the circumference of the funnel will run down into the tube and cause
the cork to float, and tho quantity of water in the tube may be seen by tho
hci<ffit to which the stem of the float is raised. Tho stem of the float is so
graduated as to show by its divisions the number of perpendicular inches of
wator which fell on the surface of the earth since the last observation. After
every observation the cylinder must be emptied.
1440. A copper funnel forms another very simple rain-gauge : tho area of the opening
must be exactly ten square inches. Let this funnel be flxcd in a bottle, and tho quantity
of rain caught is ascortainod by multiplying tho weight, in ounces, by 173, which gives
the depth in inches and parts of an ineli.
1441. In fix in g these gauges, care must bo taken that the rain may have free access to
th em ; hence the tops of buildmgs are usually tho best places; though some concoivo
that the nearer the rain-gauge is placed to the ground the more rain it wiU collect.
1442. In crrder to compare the quantities o f rain collected in pluviometers at different
places, the instruments should be fixed at the same heights above the ground in all such
pla ces; because, at different heights, the quantities are always different, oven at tho
same place.
1443. Thermometer. As the weight of the atmosphere is measured by the barometer,
so tho thermometer shows the variations in tho temperature of the weather; for ovevy
change of the weather is attended with a change in the temperature of the air, which a
thermometer placed in the open air will point out, sometimes before any alteration is perceived
in tho bai'omotcr. . , , „
1444. The scales o f different thermometers m e as follow In Fahrenheit s the freezing
point is 32 dogi-ees, and tho boiling point 212 degrees. In Ecanmur’s, the freezing
point is 0, and tho boiling point 80 degrees. In the centigrade thermometer, wliich is
generally used in Franco, and is the samo as that of Celsius, which is the thermometer of
Sweden, the ft-oezing point is 0, and the boiling point 100 degrees. As a i-ulo for comparing
or reducing these scales, it may be stated that 1 degree of Ecaumiir’s scale contains
2 ) degrees of Falircnheit; and to convert tho degrees of the one to the other, the rule is
to multiply by 9, divide by 84, and add 32. Ono degree of the centigrade scale is equal
to one degree and eight tenths of Fah ren h eit; and the n d e here is, to multiply by 9,
divide by 6, and add 32. Any of these thermometers may he proved by immersing it
in pounded ice for the freezing point, and in boilmg water for tho boiling p o in t; and if
the space between these points is equally divided, the thermometer is correct,
1445. The study ofthe weather from precedent, affords useful hints as to the clnu'actcr
of approaching seasons. From observing the general character e>f seasons for a long
period, certain general results may bo deduced On this principle, Kirwan, on comparing
a number of observations taken in England from 1677 (Trans. Irish Acad.) to
1789, a period of 112 years, found : —
That when there has been no storm hefare or after the vernal equinox, tho ensuing
summer is gencraUy dry, at least five times in six.
That when a storm happens from an easterly point, either on the 19th, 20th, or 21st of
May, the succeeding summer is generally dry, at least four times in five.
That when a storm arises on the 25th, 26th, or 21th o f March, and not before, in any
point, the succeeding summer is generally dry, four tinie.s in five.
I f there be a storm at S. W. or W. N. IF., on the 19th, 20th, 21st, or 22d of March,
the succeeding summer is generaUy wet, five times in six.
In this countiy, winters and springs, i f diy, are most cammmily cold; i f moist, warm ;
on the contrary, dry summers and autumns are usually hot, and moist summers cold ; so
that, if we know the moistness or dryness of a season, we can form a tolerably accurate
judgment of its temperature. In tliis country, also, it generally rains less in March
than in November, in the proportion, at a medium, of seven to twelve. It generally
rains less in April than October, in the proportion of one to two, nearly at a medium.
I t generaUy rains less in May than September : the chances that it does so are at least
four to three ; but, when it rains plentifully in May, as 1-8 inches or more, it generally
rains but little in September ; and when it rains one inch, or less, in May, it rains plonti-
fnlly in September. , . , , ,
1446. The probalilities o f particular seasons being followed by others, have heen ealanlated
by Kinvan ; and, although his rules cliiefly relate to the climate of Ireland, yet, as
there exists but little difference between that island and Great Britain in the general
appearance of the seasons, we shall mention some of his conclusions.
1447. In forty-one years there were six wet springs, twenty-two dry, and thirteen
variable; twenty wet summers, sixteen dry, and five variable; cloven wet autumns,
eleven diy, and nineteen variable.
. T IIE ATMOSP IIEEE.
1448. A season is accounted wet when it contains two wet months. In general, the
quantity of rain which falls iu dry seasons is less than five inches ; in wet seasons more. .
Variable seasons are those in which there fall between thirty pounds and thirty-six
pounds, a pound being equid to '157639 of an inch.
1449. .lanuary is the coldest month in every latitude ; and Ju ly is the wannest month
in all latitudes above forty-eight degrees : in lower latitudes, August is generally the
warmest. The difference between the hottest and coldest months increases in proportion
to the distance from the equator. Every habitable latitude enjoys a mean heat of
sixty degrees for at least two months ; which heat is necessary for the production of
corn.
Sect. III. O f the Climate o f Britain.
1450. The climate ofthe British isles, relatively to others in tho samo latitude, is temperate,
liiiinid, and variable. The moderation of its temperature, and its humidity, are
owing to our being suiToundcd by w a te r; which, being less affected by the sun than the
earth, imbibes less heat in summer ; and, from its fluidity, is less easily cooled in winter.
As the sea on our coast never freezes, its temperature must always he above 33° or 34°;.
and hcncc, when air from the polar regions, at a much lower temperature, passes over it,
that air must be in some degi'cc heated by the radiation from the water. On the other
hand, in summer, the wann cuiTonts of air from the south nccessai-ily give out part of
their heat in passing over a surface so much lower in temperature. The variable natui-e
of our climate is chiefly owing to the unequal breadths of wateiy surface whicli surround
u s : on ono side, a channel, of a few leagues in b re ad th ; on the other, the Atlantic
Ocean. The temperature of the British seas rarely descends below 53° or 54°.
1451. The British climate varies materially within itself: some districts are diy, as the
o a st; others moist, as the west co a st; in tho northern extremity, dry, cold, and windy ;
in the south, warm and moist. Even in moist districts, some spots are exeessivcly diy,
as part of Wigtonshfre, from the influence of tho Isle of Man in warding off tho wateiy
clouds of tho A tlan tic ; and, in diy districts, some spots are moist, from the influence of
high mountains in attracting and condensing clouds charged with wateiy vapour. The
mean tcmpcratiuo of London equals 60° 3 6 '; that of Edinburgh equals 47° 8 4 '; and
the probable mean temperatm'c of all Britain will equal 48°. The usual range of the
barometer is within three inches. The mean annual rain is probably about 32 inches.
Tho climate is variable, and subject to sudden alternations of heat and cold, which are
supposed to render pulmonary complaints common with u s ; but, on the whole, it is
h ea lthy; and the moisture of our clouded atmosphere clothes our fields with a lasting
verdure, unknown to the more favoured regions of southern Eiu-ope. (T .)
1462. The deterioration o f the British climate is an idea entertained by some; but,
whether hi regard to general regularity, temperature, moisture, or wind, the alleged
changes arc unsupported hy satisfactoiy proofs. I t is not improbable but the humidity
of our climate, as Williams alleges (Climate o f Britain, §•«, 1816), has of late years been
increased hy the increase of evaporating surfaces, produced hy the imiltiphcity of hedges
and plantations; a surface covered with leaves being found to evaporate considerably
more than a naked surfiice. I f the humidity of tho climate were greater before the
drainage of morasses and the eradication of forests for agi-icultural puiqioses, a comparative
rctui-n to the same state, by artificial planting and in'igation, must have a
tendency to produce tho same results. However, it will be long before the in'igation of
lands is can-iod to such a degree as to produce the iiisalubi-ious effects of undrained
morasses : and as to our woods and hedges, we must console ourselves with the beauty
and the shelter which they produce, for the increase of vapour supposed to proceed from
them. Many arguments in favour of tho belief that a change has taken place in tho
British climate, have been drawn from old books on horticultxu-e, in which seeds are
directed to be sown at seasons when we know they would now perish ; and frait is said
to ripen in months when it is now never ripe. In Evelyn’s Ni/fco, published in 1664,
wo are infoi-mcd that chen-ies, strawbei-ries, &c., were ripe in the open gi-ound in M a y ;
raspberries, corinths (cun-ants), melons, &c., in J u n e ; aud peaches, ncctai-ines, and
plums, in Ju ly and A u g u st; and oven after making allowance for the fact that, before
the change of stylo. May extended to what is now the middle of the second week in
June, we shaU find that these fraits are now full a fortnight or three weeks later in
ripening than they were in Evelyn’s time. Some curious remarks on the change of
climate in Britain during the last thirty years of the eighteenth century may be found in
Gametes Tour through the Highlands o f Scotland in 1800, and in Pinherton’s Geography,
vol. i. p. 70. Both these writers assert that the British climate is now more cold and
moist than it was formerly; but in an article in the Edinburgh Iteview, vol. xxx. p. 1.,
on “ Polar Ice, and a North West Passage,” it is asserted that no material change has
taken place in the climate of Europe for the last 1000 years.
G G