258 M, Humboldt on Isothermal Lhies^ and the 
order to find the same quantity of annual heat as in America 
As a place could not be found in the Old World, whose mean 
temperature was 48° the same as that of Williamsburg, I have 
supplied it with an interpolation between the latitudes of two 
points whose mean temperatures are 56°.5 and 59° 4. By an 
analogous method, and by employing only good observations, I 
have found that 
1. The isothermal line of 32® (0® centig.) passes between Uleo and Enontekies 
in Lapland (lat. 66° to 68°; East long, from London 19° to 22°), and Table Bay in 
Labrador (lat. 54° O', west long. 58°.) 
2. The isothermal line of 41° (5° centig.) passes by near Stockholm (lat, 60° 
east long. 18°) and the Bay of St George in Newfoundland (lat. 48°, and long. 59” ) 
3. The isothermal line of 50° (10° centig.) passes by Belgium (lat. 51°, east long, 
2°) and near Boston (lat. 42° 30', west long. 70° 59.) 
4. The isothermal line of 59° (1 5° centig.) passes between Rome and Florence 
(lat. 43° O', east long. 11° 40') and near Raleigh in North Carolina (lat, 36* O', ^and 
west long. 76° 30'.) 
The direction of these lines of equal heat, gives for the two 
systems of temperature, which we know by precise observations, 
viz. part of the middle and west of Europe, and that of the 
coast of America, the following differences : 
4- 
Latitude. 
Mpn Temp, of the west 
of the Old World. 
Mean Temp, of the east 
of the New World. 
Difference. 
30 
70°.52 
66°.92 
3\60 
40 
63.14 
54.50 
8.64 
50 
,50.90 
37.94 
12.96 
60 
40.64 
23.72 
16.92 
If we call the mean equatorial temperature 1, we shall have 
the half of this temperature in the Old World at 45°, and iq 
the east of the New World, at 39° of lat 
The mean temperatures decrease 
Latitude. 
Temi>. 
Temp. 
’o° — 20° 
r 1 
p 3°. 6 
20 —30 
7.2 
10.8 
.30 —40 
In the Old 
7.2 
In the New 
12.6 
40 —5b 
' \yorld, 
12.6 
' World, ' 
16.2 
50 —60 
9.9 
133 
0 —60 J 
40.5 J 
- 56.5 
In both continents, the zone in which the mean ternperature 
aecreases most rapidly is coniprehepded between the parallels of 
* This observation relates to the Centigrade scale. If we count the tempera^ 
tures from 32°^, it applies also to Fahrenheit’s scale. — 
