Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 13, MAT-MIC

Phil.
Mug vol.
vii* P 355
710 M E T E O
phylical fenfe, from the water, chiefly in poffefling left
the Air. gravity > and ^ is demonftrated a priori on the princx-
U--Y PIes.of the Newtonian philofophy, that it ought to have
its tides as well as the ocean, although in a degree as
much lefs perceptible as is its gravity.
He fuppofes, therefore, that the joint attra&ions of
the fun and moon at the new moon, and the attraction of
the moon predominating over the fun’s weaker attrac¬
tion at the full, tend to deprefs the barometer, by tak¬
ing off from the gravity of the atmofphere, as they
produce a high tide in the waters, by taking off from
their gravity; and, again, that the attra&ion of the
moon being djminilhed by that of the fun at her quar¬
ts rs, this diminution tends to make a high barometer,
together with a low tide, by permitting each fluid to
prefs with additional gravity upon the earth
'Chap. II. Of the Changes which take place in the
‘Temperature of the Air.
It is obvious to the mofl: carelefs obferver, that the
temperature of the air varies confiderably even in the
fame place, and at the fame feafon. This conftant va¬
riation muft be attributed to the reflefted rays of the
fun, which communicate heat from the furface of the
earth to the furrounding atmofphere. As from this
eaufe the heat of thofe places which are fo fituated as
to be mofl: warmed by the fun’s rays is always greateft,
and as this temperature varies in every place with the
feaion of the year, and diminifties according to the
height of the ajr above the furface ; and as the earth
ac the equator is expofed to the mofl: perpendicular rays
of the fun, the. earth is there hotteft, and its heat dimi-
niflies gradually from the equator to the poles. Of
courfe, the temperature of the air muft vary in the fame
manner, being hotteft over the equator, and diminifti-
ir.g in temperature towards the poles, where it is cold-
eft. Though it is hotteft at the equator, its heat, as
in all other fituations, gradually diminifties there, as wre
afeend above the furface of the earth.
R O L 0 G Y- Chap. n.
1 hough there is a confiderable difference in every Temper-
part of the w orld between the temperature of the at- of
mofphere in fummer and in winter; though in the fame ike Air-
feafon the temperature of almoft every day, and even
every hour, differs from that which precedes and fol¬
lows it; though the heat varies continually in the moft
irregular and feemingly capricious manner ftill there
is a certain mean temperature in every climate, which
the atmolphere has always a tendency to obferve, and
which it neither exceeds nor comes Ihort of beyond a
certain number of degrees. What this temperature is,
may be known by taking the mean of tables of obferva-
tions kept for a number of years ; and our knowledge
of it muft be the more accurate the greater the number
of obfervations is.
The mean annual temperature is greateft at the equa- Meant*
tor (or at leaft a degree or two on the north fide of it),nual tem!
and it diminiflies gradually towTards the poles, where itpefature
is leaft. This diminution takes place in arithmetical ?reateftat
progrefiion, or, to fpeak more properly, the annual!hc c<ltla'
temperatures of all the latitudes are arithmetical means ‘
between the mean annual temperature of the equator
and that of the pole. This was firft afeertained by Mr
Meyer ; and Dr Kirwan improving on Meyer’s hint
has calculated in the following table the mean annual
temperature of every latitude between the equator and
the pole. It muft be remarked, however, that this
table is calculated only for a particular part of the
earth s furface, viz. that part of the Atlantic ocean
which lies betAveen the 8o* of northern, and the 450 of
fouthern latitude, extending weftward as far as the Gulf
ftream, and to within a few leagues of the coaft of A-
merica, and for all that part of the Pacific ocean thait
reaches from 450 of north latitude to 4c1* of fouth lati¬
tude, and extending between the 20th and 275th de¬
gree of longitude eaft from London. This part of the
ocean is called by Dr Kirwan the ftandard, and was
beft fuited to his purpofe, as the reft of the ocean is
fubjedl to irregularities, which will be noticed prefent-
ty (D)-
Lat.
90
89
88
87
86
85
84
83
82
81
80
79
78
Temper,
31*
31.04
21.10
S'-H
31.2
3i-4
3M
3i-7
32.0
32.2
32.6
33.9
33-2
Lat
77
76
75
74
73
•7 2
7i
70.
69
68
67
66
65
Temper.
Lat.
33- 7
34*1
34- 5
35- o
35*5
36.0
36.6
37-2
37-8
38.4
39*1
39-7
40.4
64
63
62
61
60
59
58
57
56
5?
54
53
52
Temper.! Lat.
41.2
4I*9
42.7
43- 5
44- 3
45- °9
45-8
46.7
47-5
48.4
49.2
50.2
51*1
51
5°
49
48
47
46
45
44
43
42
4*
40
39
Temper.
52-4
52-9
53.8
54*7
5 5-6
56.4
57-5
58.4
59-4
60.3
61.2
62.0
63.0
Lat.
38
37
36
35
34
33
32
31
30
29
28
27
26
Temper.
Lat.
63.9
64.8
65-7
66.6
67.4
68.3
69.1
69.9
70.7
71- 5
72- 3
72.8
73- 8
25
24
23
22
21
20
J9
18
x7
16
!5
M
*3
Temper.
74- 5
75- 4
75- 9
76- 5
77.2
77.8
78- 3
78.9
79- 4
79-9
80.4
80.8
81.3
Lat,.
12
II
10
9
8
7
6
5
o
T
emper
81.7
82.0
82.3
82.7
82.9
83.2
83-4
83.6
84.0
Dr
(d) In calculating this table, Dr Kirwan proceeded on the following principle. Let the mean annual heat at
the equator be m and at the pole w—« ,• put (p for any other latitude ; the mean annual temperature of that lati¬
tude will be *»--« xfin. . If, therefore, the temperature of any two latitudes be known, the value of m and n
mzj be found. Now, the temperature of north latitude 40° has been found by the beft obfervations to be 62. i°,
5 and