406 
ON THE SOURCES OF HEAT WHICH INFLUENCE CLIMATE. 
We have now seen that the heat which influences our climates may be traced 
to the four following sources : 
1. The calorific power of the solar rays, which are well known to vary directly 
with the latitude. 
2. The temperature of the planetary spaces, which apply equally to every 
portion of the earth’s surface. 
3. The heat of the central mass of our earth. 
4. The caloric changed by every variation from one state to another. 
Of these sources of heat the two first govern, for the most part, our various 
climates; besides their influence, it is scarcely necessary to add that other cir¬ 
cumstances have much effect on climate, as, for example, the hygrornetric state 
of the atmosphere, the proximity of other continents, the prevailing winds, the 
character of the soil, and several others that form of themselves a distinct branch 
of inquiry, but which it is not necessary for me now to enter upon. Their effects 
are at once made obvious by referring to the isothermal lines, or lines of equal 
temperature traced by Humboldt, which can be shewn to deviate much from the 
parallels of latitude. 
In Europe the position of places with the same annual heat does not differ more 
than eight or nine degrees, but the difference of those having the same winter 
temperature is not less than 18 or 19 degrees. The winter of Scotland is as mild 
as Milan in North Italy. Ireland is remarkable for mild winters and cold sum¬ 
mers. The mean temperature in Hungary for the month of August is 71^ 
degrees ; while in Dublin for the same month it is only 60^ degrees. New York 
has the summer of Rome and the winter of Copenhagen. Quebec has the 
summer of Paris and the winter of St. Petersburg. In the same manner, at Pekin, 
which has the mean temperature of Britain, the heat of summer is greater than at 
Grand Cairo in Egypt; and the cold in winter as severe as at Upsal, in Sweden. 
These inequalities are due to a complex set of phenomena which regulates the 
machinery of climates. It is uncertain if we shall ever be permitted to view 
this machinery; but there can be little doubt that we should there see the same 
system of compensation for apparent irregularities as the imperishable labours of 
Newton and La Place have shewn to us in the movements of the heavenly 
bodies; and which there are ample reasons for our supposing to extend to all the 
other works of Nature. 
£The object of The Naturalist , as expressed in the title-page, and as carried 
out in the body of the work, is to illustrate the animal, vegetable, and mineral 
kingdoms. But we feel assured that neither our readers nor ourselves can object 
to an occasional digression into collateral branches of Natural Science. Or did 
such a scruple exist, surely it would altogether vanish on perusal of any paper so 
interesting and so ably written as the preceding.— Ed.] 
