xviii President's Address 



for it is only now that we are beginning to obtain clear 

 ideas of the complex laws to which the movements and 

 changing conditions of onr atmosphere are subject. The 

 result of the systematic work I refer to is the establishment 

 of certain " laws" or generalisations of the conditions and 

 movements of the atmosphere which appear to prevail at 

 different parts of the earth's surface. These have been 

 treated of by several recent writers on meteorology, but I 

 believe most clearly and succinctly in a valuable little 

 pamphlet by the Rev. Clement Ley, issued by the meteoro- 

 logical department of Great Britain. These may be stated 

 as follows : — As regards pressure or normal height of 

 barometer, our atmosphere may be divided into five great 

 regions ; a belt of moderately low pressure occupies the 

 equatorial regions, north and south of this are two belts of 

 high pressure, and north and south of these again we find 

 areas of low pressure in the polar regions. These areas 

 alter, however, with the seasons, being largely influenced by 

 the solar heat, and we find this remarkable result — in the 

 winter of either hemisphere the temperate zone belt of high 

 pressure is continuous over land and sea. In the summer, 

 however, the belt is broken up by all the continents 

 becoming covered by areas of low pressure. Although 

 Australia lies in the southern belt of high pressure, and is 

 normally covered by an area of high pressure in winter, in 

 summer, under the influence of increased solar heat, the 

 equatorial region of low barometer extends southwards and 

 embraces Australia, while on the ocean east and west of us 

 the normal high pressure of the temperate belt prevails. 

 The same occurs with Africa and South America, where 

 similar areas of low pressure prevail during the summer 

 months, while in the Northern Hemisphere high pressures 

 prevail generally over land and sea in the temperate zones, 

 and, in fact, extend almost to the polar regions north of the 

 land in Asia and America. It has also been established 

 that the movements of the atmosphere are subject to certain 



