5 
Bistribution of Heat over the Globe. 
The temperature of the atmosphere, and the magnetism of 
the globe, cannot, like those phenomena which depend on one 
cause, or on a single centre of action, be disengaged from the 
influence of disturbing circumstances, by taking the averages of 
many observations in which these extraneous eflects are mutually 
destroyed. The distribution of heat, as well as the dip and va- 
riation of the needle, and the intensity of the terrestrial mag- 
netism, depend, by their nature, on local causes, on the consti- 
tution of the soil, and on the particular disposition of the radiat- 
ing surface of the globe. We must, however, guard against 
confounding under the name of extraneous and disturbing causes, 
those on which the most important phenomena, such as the dis- 
tribution and the more or less rapid developement of organic 
life, essentially depend. Of what use would it be to have a table 
of magnetic dips, which, in place of being measured in parallels 
to the magnetic equator, should be the mean of observations 
made on the same degrees of terrestrial latitude, but under dif- 
ferent meridians ? Our object is to ascertain the quantity of 
heat which every point of the globe annually receives, and, what 
is of most importance to agriculture, and the good of its inha- 
bitants, the distribution of this quantity of heat over the diffe- 
rent parts of the year, and not that which is due to the solar 
action alone, to its altitude above the horizon, or to the dura- 
tion of its influence, as measured by the semidiurnal arcs. 
Moreover, we shall prove, that the method of means is unfit 
for ascertaining what belongs exclusively to the sun, (inasmuch 
as its rays illuminate only one point of the globe,) and what is 
due both to the sun and to the influence of foreign causes. 
Among these causes maybe enumerated the mixture of the tem- 
peratures of different latitudes produced by winds; — the vicini- 
ty of seas, which are immense reservoirs of an almost invariable 
temperature ; — the shape, the chemical nature, the colour, the 
radiating power and evaporation of the soil ; — the direction of 
th^e chains of mountains, which act either in favouring the play 
of descending currents, or in affording shelter against particular 
winds ; — the form of lands, their mass and their prolonga- 
tion towards the poles ; — the quantity of snow which covers them 
in winter, their temperature and their reflection in summer ; — 
and, finally, the fields of ice, which form, as it were, circumpolar 
