90 REPORT—1848, 
As provisional values, I find— Reaumut. Fahrenheit. 
January. Northern Hemisphere.......+ 75 48°8 
Southernescsvsrececesscess 12:2 59.5 
The Globecssice.s-o0 . 9°9 54°15 
July. Northern Hemisphere........ 17°3 71‘0 
Southern .....seeseeeee.. + 96 —-63°6 
The Globe... 22.5.2... 13°5 62°3 
The temperature of the whole globe increases therefore fully 34 degrees of 
Reaumur, or 8 degrees of Fahrenheit, from January to July. If we take the 
mean between these months, we have as the mean temperature of the globe, 
11°7 Reaumur, or 58°*2 Fahrenheit; as the mean temperature of the north- 
ern hemisphere 12°°4 Reaumur, or 60° Fahrenheit; and of the southern 
hemisphere 10°°9 Reaumur, or 56°°4 Fahrenheit. As when we move south- 
wards we see the northern constellations sink and the southern rise above the 
horizon, so the sun on entering new signs in his annual course, overlooks 
constantly new portions of the earth’s surface. This surface being a highly 
varied one, the sun’s influence on it is also constantly varying, for the 
impinging solar heat is employed in raising the temperature of substances 
which do not change their condition of aggregation ; but when engaged in cau- 
sing the melting of ice or the evaporation of water, it becomes latent. When 
therefore the sun returning from its northern declination enters the southern 
signs, the increasing proportion of liquid surface upon which it shines causes 
a corresponding part of its heat to become latent; and hence arises the great 
periodical variation in the temperature of the whole globe, which has been 
noticed above. 
These relations appear to contain within themselves an important mo- 
tive force in the machinery of the whole atmosphere, for they are condi- 
tions on which a periodical transition of aqueous vapour into a liquid state 
depends. The circulation of moisture, which acts so importantly on all 
vegetable and animal life, thus appears no longer dependent on merely local 
effects of cooling, or the intermixture of currents of air of unequal tempe- 
rature; the non-symmetrical distribution of land and sea in the two hemi- 
spheres necessarily causes the aqueous vapour, which is developed in a pre- 
ponderating degree over the southern hemisphere from the autumnal to the 
vernal equinox, to return to the earth in the form of rain or snow during 
the other half of the year. Thus the wonderful march of the most power- 
ful steam-engine with which we are acquainted, the atmosphere, appears per~- 
manently regulated by laws of periodical action. 
Men often complain that all physical circumstances are irregularly distri- 
buted over the earth’s surface ; but this very irregularity is, as we have just 
seen, a preserving principle of the whole terrestrial life. 
It is probable that the northern hemisphere acts as the condenser, and 
the southern hemisphere as the water reservoir of this steam-engine ; and thus 
that a greater quantity of rain falling in the northern hemisphere is one cause 
of its higher temperature, since the heat which became latent in the southern 
hemisphere is set free in the northern in heavy falls of rain. 
But if all these phenomena are essentially connected with the proportion 
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