in different parts of the Globe. 125 



of the Icy Sea itself could hardly be assumed as its boundary. 

 A greatly diminished atmospheric pressure taking place in 

 summer over the whole continent of Asia must produce an 

 influx from all surrounding parts ; and thus we have west 

 winds in Europe, north winds in the Icy Sea, east winds on 

 the east coasts of Asia, and south winds in India. The mon- 

 soon itself becomes, as we see, in this point of view, only a 

 secondary or subordinate phenomenon. 



I have endeavoured to establish the reality of the above 

 phenomenon and its climatological bearings, in several 

 memoirs ; and I must refer for the numerical values to 

 Poggendorff's " Annalen," lviii., p. 117 ; lxxvii., p. 309 ; and 

 to the " Berichte" of the Berlin Academy, 1852, p. 285. 

 I will here embody the results in distinct propositions, in 

 order to shew, in connection therewith, the importance of the 

 bearing of the Hobarton observations. 



1. At all stations of observation in the torrid and tempe- 

 rate zones, the elasticity of the aqueous vapour contained in 

 the atmosphere increases with increasing temperature. In 

 the region of the monsoons this increase from the colder to 

 the warmer months is greatest near their northern limit. 

 Hindostan and China present in this respect the most exces- 

 sive climate. No differences of similar magnitude are found 

 in the southern hemisphere. The form of the curve of elas- 

 ticity of the aqueous vapour shews, however, a less decidedly 

 convex summit in the region of the monsoons than beyond 

 it, having in that region rather the character of a flattened 

 summit or table-land, the elasticity continuing nearly the 

 same throughout the period of the rainy monsoon. Near 

 the equator the convex curve of the northern hemisphere 

 becomes gradually, first flattened, and then transformed into 

 the concave curve of the southern hemisphere. In the 

 Atlantic this transition takes place in a rather more northerly 

 parallel. In regard to the magnitude of the annual varia- 

 tion, the following rule appears generally applicable in the 

 torrid zone ; the annual variation is considerable at all 

 places where equatorial currents prevail when the sun's alti- 

 tude is greatest, and polar currents when the sun's altitude 

 is least; and inconsiderable, wherever the direction of the 



