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

.Chap. II.
Tempera¬
ture of
the Air.
Lat.
Ou
5
io
20
25
3°
35
40
Mean height
of the term of
congelation,
in feet.
,5577
J5457
15067
14498
I3719
13050
11592
10664
9016
Lat.
45
5°
55
60
6 5
70
75
80
METEOROLOGY.
From the modes of eftimating the diminution of tem¬
perature now given, which agree extremely well with
Mean height
of the term of
congelation,
in feet.
7658
6260
4912
3684
2516
*557
748
120
7r3
Tempera¬
ture of
the Air.
This laft height of 120 feet M. Bouguer called the
lower term of congelation. He alfo diilinguilhed an¬
other term of congelation above which no vifible va¬
pour rifes, and this he called the upper term of congela¬
tion. This line is confidcred by Kirwan as much lefs
variable during the fummer months than the lower line,
and it has therefore been adopted by him to determine
the rate of diminution in the temperature as we
afeend into the atmofphere. He has calculated its
height for every degree of north latitude in the follow¬
ing table.
\r. Lat,
O
5
6
7
8
9
10
11
12
*3
*4
*5
16
*7
18
*9
20
21
22
23
24
25
Feet.
2800 c
27731
27649
275°j
27364
27224
2708
26880
26676
26472
26268
26061
25781
>55°*
25.221
24941
24661
24404
24*47
23890
23633
23425
N. La-
26
27
28
29
3°
3*
32
33
34
35
S6
37
38
39
40
4*
42
43
44
45
46
47
I eet.
22906
22389
21872
2*3 55
20838
2049 2
20146
19800
*9454
19169
18577
17985
*7393
168' 1
16207
*57*2
15217
14722
14227
*3730
*323 :
12740
4. Lai.
4"
49
50
5*
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
Feet.
12245
II750
**253
10124
8965
7806
6647
56*7
5933
5439
5345
5251
5*48
5068
4989
49*01
483*:
47 5 2!
46841
4616;
4548'
4480!
N. Lat
70
7*
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
Feet.
44*3
4354
429 5
4236
4177
4*'9
4067
40*5
3963
39**
3861
38.5
3769
3723
3677
3631
3592
3 3 93
35*4
1475
34321
(F)
obfervation, we find that the temperature diminiihes in
arithmetical progreffion, and hence we infer that the 19
temperature of the air at a diftance from the earth Fempera-
is owing to the conducing power of the air, and not^®®^®
to the afeent of hot air from the furface of the the earth
earth. * owing to
It is however found that in winter the upper flratathe con-
of the air are often warmer than the lower •, and this
fuperior heat, almoft conftantly obferved in winter, is^e
attributed by Hr Kirwan to a current of warm air from
the equator, rolling towards the north pole during our
winter *.
Irijh
VOL. XIII. Part 11.
We have now given the general method of finding
the medium annual temperature all over the globe 5 but^ ^75.
there are feveral exceptions to our general inferences
which mull be particularly mentioned. 20
That part of the Pacific, ocean which lies between Tempera-
north latitude 52° and 66° is no broader at its northern
extremity than 42 miles, and at its fouthern extremity c^c ocean.
its breadth fcarcely exceeds 1300 miles : it is reafon-
able to fuppofe, therefore, that its temperature will be
confiderably influenced by the furrounding land, which
confifls of ranges ol mountains, covered a great part of
the year with fnow 5 and there are befides a great many
high, and confequently cold, iflands leattered through it.
For thefe reafons Hr Kirwan concludes, that its tempe¬
rature is at leaf! 40 or 50 below the ftandard. Bui we
are not yet furnilhed with a fufficient number of obfer-
vations to determine this with accuracy. 2I
It is the general opinion, that the fouthern hemi-Ofthe
fphere beyond the 40° of latitude is confiderably colder 0; tbt'rn
than the correfponding parts of the northern hemifphere. ''uu 'l- ‘clc
See America. 22
Small feas furrounded with land, at leaf! in temperate Of fmall
and cold climates, are generally warmer in fummer andiea8<
colder in winter than the flandard ocean, becaufe
they are much influenced by the temperature of the ^
land. The gulf of Bothnia, for inftance, is for the
mofl part frozen in winter •, but in fummer it is feme-
times heated to 70°, a degree of heat never to be found
in the oppofite part of the Atlantic. 1 he German fea
is above 30 colder in winter, and 50 warmer in fummer,
than the Atlantic. The Mediterranean fea is, for the
greater part of its extent, warmer both in fummer and
winter than the Atlantic, which therefore flows into it.
The Black fea is colder than the Mediterranean, and
flows into it.
The eaftern parts of North America are much colder
than the oppofite coalt of Europe, and fall Ihort of the
4 X ftandard
(f) Hr Kirwan has given us the following rule for afeertaining the temperature at any required height, fup-
pofing we know the temperature of the furface of the earth.
For the temperature obferved at the furfaee of the earth, put m ; for the given height h, and t for the height
of the upper term of congelation at the given latitude 5 then — — the diminution of temperature for
100
every ICO feet of elevation 5 or it is the common difference of the terms of the progreffion required. Let this
common difference thus found be denoted by c ; then cX 7^ gives us the whole diminuTon of temperature
from the furface of the earth to the given height. Let this diminution be denoted by d, then m—d is obvioufly,
the