S64 
M. Humboldt on Isothermal Lines ^ 
lities. 1 shall not mention the island of St Helena, Lat. 15® 
55' whose mean temperature, acco^'ding to the observations of M. 
Beatson, at the sea side, does not exceed 71°6 or It is 
the eastern coast of America, which, in the observations of a Por- 
tuguese astronomer, M. Benito Sanchez Dorta present us with 
the S. Lat. of 22° 54', almost at the limit of the equinoctial 
region with a plan, of which we know the climate by more than 
8500 thermometrical and barometrical observations made every 
year, to ascertain the horary variations in the heat and pressure 
of the air. The mean temperature of Bio Janeiro is only 74*.3, 
whilst, notwithstanding the north winds which bring the cold 
air of Canada during winter into the Gulf of Mexico, the mean 
temperatures of Vera Cruz, (Lat. 19° 11',) and of the Havannah, 
(Lat. 28° 10',) are 77°.9. The differences of the two hemis- 
pheres become more sensible in the warmest months. 
Rio Janeiro. 
Mean Temp. 
June, 68°.0 
July, 70 2 
January, 79 2 
February, 80 6 
Havannah. 
Mean Temp. 
December, 71°.8 
January, 70 2 
J uly, 88 8 
August, 88 8 
The great equality ' in the division of the annual heat in 
84° of N. and S. Lat. is very surprising. If we attend to the 
three continents of New Holland, Africa and America, we shall 
find, that the mean temperature of Port Jackson, (Lat. 88° 51',) 
is, after the observations of MM. Hunter, Peron, and Freyci- 
net, - - - 66°.7 
That of the Cape of Good Hope, (Lat. 88° 58',) 66 9 
That of the city of Buenos Ayres, (Lat. 84° 86',) 67 5 
In the northern hemisphere 60°. 8 or 69° 8 of annual tem- 
perature corresponds to the same latitude in the northern 
hemisphere, according' as we compare the American system of 
climates f or the Mediterranean one;— rtlie concave or the convex 
* Menu de VAcad. de Lisbonne^ tome ii. p. 34>8. 369, 
Latitude, Mean Temp. 
31° 28', 64*.8 
39 06, 53.8. 
-f* Natchez, 
Cincinnati, 
