METEOROLOGY. 
17 * 
TABLE of the Monthly Mean Temperature, &c. ctnllnued. 
Lat. 
January 
February 
March 
April 
May 
June 
July 
August 
September 
October 
November 
December 
26® 
25° 
24° 
23° 
22° 
21° / 
20° 
19° 
13° 
17° 
16° 
15° | 
14° 
13° 
12® 
11 ® 
10* 
64.5 
65.5 
67. 
68. 
69. 
71. 
72. 
72.5 
73. 
73.5 
74. 
74.5 
75. 
76. 
76.5 
77. 
77.5 
7q.5 
71. 
72. 
79, 
72.5 
74. 
75. 
76. 
76.5 
77. 
77.5 
78. 
78.5 
79. 
79.5 
/ 9.8 
80. 
73. 
73.5 
74.5 
75. 
75.5 
76. 
77. 
77.5 
78. 
78.5 
79. 
79.5 
80. 
80.8 
8 1 . 
81.5 
81.3 
73.8 
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 
81.7 
82. 
82.3 
77.5 
78. 
78.5 
79.5 
80. 
80.5 
81. 
81.5 
82. 
82.5 
S3. 
83*. 
83.5 
84, 
84. 
76.5 
78.5 
79. 
79.5 
80. 
80,5 
81.5 
82. 
82.5 
83. 
83.5 
83.8 
84. 
84.3 
84.6 
84.8 
76.5 
78. 
78 .5 
70 
79.5 
80. 
80.5 
81.5 
82. 
82.5 
83. 
83.5 
83.8 
84. 
84.3 
84.6 
84.8 
76.5 
78. 
78.5 
79. 
79.5 
80. 
<80.5 
81.5 
82. 
82.5 
83. 
83.5 
83.8 
84. 
84.3 
84.6 
84. & 
76.5 
77.5 
78. 
78.5 
79. 
7 9-5 
80. 
81. 
81.5 
82. 
82.5 
83. 
83. 
83.5 
84. 
84.3 
84.6 
73.5 
74.5 
75.' 
77. 
78. 
79. 
80. 
81. 
SI .5 
82. 
82.5 
83. 
83.5 
83.3 
84. 
72. 
73.5 
74. 
74.5 
75. 
75.5 
76. 
77. 
78. 
78.5 
79. 
79.5 
80. 
| 80.5 
80.8 
81. 
68.5 
69.5 
70. 
71. 
71.5 
72. 
72.5 
73. 
74. 
75. 
75.5 
76. 
76.5 
77. 
1 77.5 
78. 
78.5 
From this table it appears, that January 
is the coldest month in every latitude, and 
that July is toe warmest month in aU lati- 
tudes above 48°. In lower latitudes, August 
is generally warmest. The difference be- 
tween the' hottest and coldest months in- 
creases in proportion to the distance from 
the equator. Every habitable latitude enjoys 
a mean heat of 60° for at least two month's ; 
this heat seems necessary for the production 
of corn.. Within ten degrees of the poles, 
the temperatures differ very little; neither do 
they differ much within ten degrees of the 
equator : the temperatures of different years 
differ very little near the equator ; but they 
differ more and more as the latitudes ap- 
proach the poles. 
2. That the temperature of the atmosphere 
gradually diminishes, according to its height 
above the level of the sea, is well known. 
Tims the late Dr. Hutton, of Edinburgh, 
found, that a thermometer, kept on the top 
of Arthur’s-seat, usually stood three degrees 
lower than a thermometer kept at the bottom 
of it. Hence, then, a height of 800 feet oc- 
casioned 3° of diminution of temperature. 
On the summit of Pinchinca, the thermo- 
meter stood at 30°, as observed by Bouguer ; 
while at the level of the sea, in the same la- 
titude, it stood at 84°. Here a height of 
15564 feet occasioned a diminution ot tem- 
perature, amounting to 54°. But though 
there can be no doubt of the gradual dimi- 
nution of temperature, according to the 
height, it is by no means easy to determine 
the rate of diminution. Euler supposes it to 
be in a harmonic progression ; but this opi- 
nion is contradicted by observations. Saus- 
sure supposes, that in temperate climates the 
diminution of temperature amounts to 1° for 
every 287 feet of elevation. But Mr. Kirwan 
has shewn that no such rule holds, and that 
the rate of diminution varies with the tempe- 
rature at the surface of the earth. AVe are 
indebted to this philosopher for a very inge- 
nious method of determining the rate ot di- 
minution in every particular case, supposing 
the temperature at the surface ol the earth 
known. 
Since the temperature of the atmosphere 
is constantly diminishing as we ascend above 
the level of the sea, it is obvious, that at a 
certain height we arrive at the region of per- 
petual congelation. This region varies in 
height according to the latitude of the place ; 
it is highest at the equator, and descends gra- 
dually nearer the earth as we approach the 
poles'. It varies also according to the season, 
being highest in summer, and lowest in win- 
ter. M. Bouguer found the cold on the top 
of Pinchinqa, one ot the Andes, to extend 
from seven to nine degrees below the ireezing- 
point every morning immediately before sun- 
rise. He concluded, therefore, that the 
mean height of th‘e term ot .congelation (tire 
place where it freezes during some part of 
the day all the year round) between the tro- 
pics was 15,577 leet above the level ot the 
sea; but. in latitude 28° he placed it in sum- 
mer at the height of 13,440 feet. Now, it 
we take the difference between the tempera- 
ture of the equator and the freezing-point, 
it is evident that it w ill bear the same pro- 
portion to the term of congelation at the 
equator, that the difference between the 
mean temperature of any other degree ot 
latitude and the freezing-point bears to the 
term of congelation in that latitude. , Thus 
the following table of its height for every de- 
gree of latitude in the northern hemisphere: 
TABLE 
Of the Height of the Upper Line of Congela- 
tion in the different Latitudes of the Northern 
Hemisphere. 
between which and 32 is 40.3 : then 52 
15577 40.3 I 12072. In this manner Mr. 
Kirwau calculated the following table : 
Mean height 
of the term of 
congelation. 
Lat. &et. 
0 e- - 15577 
5 - - 15457 
10 - - 15067 
15 - - 14498 
20 - - 13719 
25 - - 13030 
30 - - 11592 
35 - - 10664 
40 - - 9016 
45 - - 7658 
50 - - 6260 
55 - - 4912 
60 - - 3684 
65 - * 2516 
70 - - 1557 
75 - - 748 
80 - - 120 
Beyond this height, which has been called 
the lower term of congelation, and which 
must vary with the season and other circum- 
stances, Mr. Bouguer has distinguished ano- 
ther, which he called the upper term of con- 
gelation; that is, the point above which no 
visible v; pour ascends. Mr. Kirwan consi- 
der: tiff line as much less liable to vary dur- 
ing the summer months than the lower term 
of congelation, and therefore has made choice 
of it to determine the rate of the diminution 
of heat, as we ascend in the atmosphere. 
Bouguer determined fhe height of this term 
in a single case, and Kirwan has calculated 
N. I 
N. 
N. 
Feet. 
Lat. 
Feet. 
Lat. 
Feet. 
Lat. 
O 
28000 ! 
33 
19800 
62 
4989 
5° 
27784 | 
34 
19454 
63 
4910 
6 
27644 j 
35 
19169 
64 
4731 
7 
27504 1 
36 
'18577 
65 
4752 
8 
27364 
37 
17985 
66 
4684 
9 
27224 
38 
17393 
67 
4616 
10 
27084 
39 
16801 
68 
4548 
11 
26880 
40 
16207 
69 
4480 
12 
26676 
41 
15712 
70 
4413 
13 
26472 
42 
15217 
71 
4354 
14 
26268 
43 
14722 
72 
4295 
15 
26061 
44 
14227 1 
73 
4236 
16 
25781 
45 
13730 
74 
4177 
17 - 
25501 
46 
13235 
7 5 
4119 
18 
25221 
47 
12740 
76 
4067 
19 
24941 
48 
12245 
77 
4015 
20 
24661 
49 
11750 
78 
- 3963 
21 
24404 
50 
11253 
79 
3911 
22 
24147 
51 
10124 
80 
3861 
23 
23890 
52 
8965 
81 
3815 
24 
23633 
53 
7806 
82 
3769 
25 
23423 
54 
6647 
83 
3723 
26 
22906 
55 
5617 
84 
3677 
27 
22389 
56 
5533 
85 
3631 
28 
21872 
57 
5439 
86 
3592 
29 
21355 
58 
5345 
87 
3553 
30 
20838 
59 
5251 
88 
3514 
31 
20492 
60 
5148 
89 
3475 
32 
20146 
1 61 
5068 
90 
3432 
The following rule of Mr. Kirwan will enable 
us to ascertain the temperature at any required 
height, provided we know the temperature at 
the surface of the earth. 
Let the observed temperature at the surface 
of the earth be — m, the height g-iven = A, and 
the height of the upper term of congelation for ' 
m — 32 
the given latitude be =: t ; then — — th* • 
Too — 1 
diminution of temperature for every hundred 
feet of elevation; or it is the common difference 
of the terms of the progression required. Let 
this common difference thus found be denoted 
by c ; then c X gives u s the whole dimi- 
nution of temperature from the surface of the 
earth to the given height. Let this diminution 
be denoted by d, then m — d is obviously the 
temperature required. An example will make 
this rule sufficiently obvious. In latitude 56°, 
the heat below being 54°, required the tempera- 
ture of the air at the height of 803 feet ? 
