§4 ' M. Humboldt on Isothermal LineSy 
In the system of European, climates, from Rome to Upsal, 
between the isothermal lines of 59° and 41% the warmest month 
adds from 16°.2 to 18° to tiie mean temperature of the year. 
Rarther north, and also in eastern Asia, and in America, where 
the isothermal lines bend towards the equator, the increments 
are still more considerable. 
As two hours of the day indicate the temperature of the whole 
day, there must also be two days of the year, or two decades, 
whose mean temperature is equal to that of the whole year. 
From the mean of ten observations, this temperature of the year 
is found at Buda in Hungary from the 15th to the SOth of 
April, and from the 18th to the S3d of October. The ordinates 
of the other decades n'iay be regarded as functions of the mean 
ordinates. In considering the temperatures of entire months, we 
find, that to the isothermal line of 35°.6, the temperature of the 
month of October coincides (generally within a degree) with 
that of the year. The following Table proves that it is not the 
month of April, as Kirwan affirms, (Estimate^ &c. p. 166.), 
that approaches nearest to the annual temperature. 
Names op 
Places. 
Mean Temperature 
Names of 
Places. 
Mean Temperature 
Of the 
Year. 
Of Oc- 
tober. 
Of 
April. 
Of the 
Year. 
Of Oc- 
tober. 
Of 
April. 
Cairo, 
72°.3 
72°.3 
77V9 
Gottingen, 
46°. 9 
47°. 1 
44°. 4 
Algiers, - 
69.8 
72.1 
62.6 
Fi'aneker, 
52.3 
54.9 
50.0 
Natchez, 
65.0 
68.4 
66.4 
•Copenhagen, 
45.7 
48.7 
41.0 
Rome, - 
60.4 
62,1 
55.4 
Stockholm, 
42.3 
42.4 
38.5 
Milan, 
55.8 
58.1 
55.6 
Christiania, 
42.6 
39.2 
42.6 
Cincinnati, 
53.6 
54.9 
56.8 
Upsal, 
41.7 
43.3 
39.7 
Philadelphia, 
53.4 
54.0 
53.6 
Quebec, 
41.9 
42 8 
39.6 
New York, 
53,8 
54.5 
49.1 
Petersburgh, 
38.8 
39.0 
37.0 
Pekin, 
54- T 
55.4 
57.0 
Abo, 
41.4 
4 .0 
40.8 
Buda, 
51.1 
52.3 
49.1 
Drontheim, 
39.9 
39-2 
34.3 
London, 
51.8 
52,3 
49.8 
Uleo, 
33.1 
37.9 
34.2 
Paris, 
51.1 
51.3 
4-8.2 
Umeo, 
33.3 
37.8 
34.0 
Geneva, 
49.3 
49.3 
45.7 
North Cape, 
32.0 
32-0 
30.2 
Dublin, 
48.6 
48.7 
45.3 
Enontekies, 
27.0 
27.5 
26.6 
Edinburgh, 
47.8 
48.2 
46.9 
Nain, 
26.4 
33.1 
27.5 
As travellers are seldom able to make observations for giving 
immediately the temperature of the whole year, it is useful to 
know the constant ratios which exist in each system of climates, 
between the vernal and autumnal temperatures, and the annual 
temperature. 
