44 
ABBE. 
Instead of rising in the torrid zone and turning back upon 
itself to antarctic regions, the southeast trade rushes across 
the equator, skirts the coasts of Africa, Arabia, India, Siam, 
and China, whirls around the great desert plateau of Tibet, 
producing the area of low pressure that is central over that 
region in the hot months, and finally is lost in Kamchatka. 
Of course this transfer of a great mass of air from the south- 
ern to the northern hemisphere during our summer must be 
followed eventually by the return of an equivalent mass to 
the southern hemisphere; but we have not yet discovered 
how 3 or when, or where that return is effected. Therein lies 
the secret of much of our so-called periodic or quasi-periodic 
and secular weather changes which depend on the internal 
mechanism of our atmosphere, not on solar or cosmic in- 
fluences. 
Finally, we now go one step further and note the fact that 
we may divide the surface of our globe into two hemispheres, 
known as the continental and the oceanic. The former has 
its pole on the Greenwich meridian at about 30° north, in- 
cluding nearly all of Europe, Asia, Africa, the Atlantic 
Ocean, and both the Americas, being about three-fourths 
land. The other has its center about 40° south ? includes the 
greater part of the Pacific, Indian, and Antarctic regions, 
and is four-fifths oceanic. The sun’s heat pours upon the 
continental hemisphere with especial fervency in May, June, 
and July, and upon the oceanic hemisphere in November, 
December, and January. The circulation of the air, both 
horizontal and vertical, the distribution of temperature, mois- 
ture and pressure, the resulting winds and rains over the 
continental hemisphere in its summer have but slight anal- 
ogy with the corresponding phenomena over the oceanic 
hemisphere in its summer, because of the differences in the 
action of insolation upon land, water, and snow or ice. We 
are no longer justified in treating the whole atmosphere as 
though it were resting upon a globe of uniform surface, and 
subject to slight perturbations by reason of ocean-currents 
and small continents. We have to consider the insolation of 
the continental hemisphere and that of the oceanic hemi- 
