( ^ ) 
Art. III. — On Isothermal Lines ^ a 7 id the Distribution of Heat 
Over the Globe. By Baron Alexander de Humboldt. 
(Continued from Vol. III. p. 274.) 
.A.FTER what has already been stated respecting the limits be- 
tween which the annual heat divides itself on the same isother- 
mal curve, it will be seen how far we are authorised to say, that 
the Coffee-tree^ the Olive^ and the Vine^ in order to be produc- 
tive, require mean temperatures of 64°.4; 60°.8, and 53°.6 Fahr. 
These expressions are true only of the same system of climate, for 
example, of the part of the Old World which stretches to the west 
of the meridian of Mont Blanch because in a zone of small extent 
in longitude, while we fix the annual temperatures, we determine 
also the nature of the summers and the winters. It is known like- 
wise, that the olive, the vine, the varieties of grain, and the fruit- 
trees, require entirely different constitutions of the atmosphere. 
Among our cultivated plants, some, slightly sendble of the ri- 
gours of winter, require very warm but not long summers; others 
require summers rather long than warm ; while others, again, in- 
different to the temperature of summer, cannot resist the great 
colds of winter. Hence, it follows, that, in reference to the culture 
of useful vegetables, we must discuss three things for each cli- 
mate, — the mean temperature of the entire summer, — that of 
the warmest month, — and that of the coldest month. I have 
published the numerical results of this discussion in my Prole- 
gomena de Distributione Geograffiica Plantarum^ secundum 
Coeli Temperiem ; and I shall confine myself at present to the 
limits of culture of the olive and the vine. The olive is cul- 
tivated in our continent between the parallels of 36'’ and 44°, 
wherever the annual temperature is from 62°.6 to 58°. 1, where 
the mean temperature of the coldest month is not Mow from 
41°.0 to 42°.8, and that of the whole summer from 71°.6 to 73°.4 
In the New World, the division of heat between the seasons is 
such, that on the isothermal line of 58°.l, the coldest month is 
• In cases like the present, we have not used the round numbers of Fahrenheit, 
as is done in the original with the Centigrade scale, but have given the real value 
of the degrees used by the author, that his exact numbers may always be ascertain- 
ed — E d. 
