322 DR ALEXANDER BUCHAN ON 



exactly the reverse in Australia of what obtains in January. Everywhere it increases on 

 advancing from the coast into inland regions. The lowest pressure, about 30*000 inches, 

 occurs near the north coast, and the highest 30 '180 inches, over the basin of the Murray 

 Eiver and its affluents. From this region the diminution of pressure continues uninter- 

 ruptedly northward as far as the summer low pressure system of Asia. Hence, the prevailing 

 winds of Australia are essentially an outflow from the high pressure region of the interior 

 towards the lower pressures of the coasts, particularly the north coast ; and the winds 

 are therefore S.E. on the north coast, S.W. at Brisbane, W.N.W. at Sydney, N. at Mel- 

 bourne, and N.E. at Adelaide. 



The high pressure of the south of Australia is continued westwards in the same 

 latitudes through the Indian Ocean. From these latitudes pressure falls continuously 

 northwards to the low pressure area in Asia ; and, as the inevitable consequence 

 of that diminution of pressure, southerly winds sweep across that ocean home into Asia. 

 Where they reach the coast after having traversed a great extent of ocean, such as the 

 coasts of India and Burmah, they precipitate a very heavy rainfall, which, from the serious 

 lowering of the specific gravity thus occasioned, has a most retarding effect on the down- 

 ward circulation of the ocean there. On the other hand, on the northern and western 

 division of the Arabian Sea the rainfall is excessively small, since the winds there have 

 traversed but a small breadth of the ocean ; and, consequently, from the dryness of these 

 winds the salinity is much increased, and the vertical circulation becomes thereby greatly 

 accelerated. 



Similarly, as pressure diminishes from about lat. 25° S. in the Pacific uninterruptedly 

 to the low pressure of Asia, the prevailing summer winds on the south-eastern coasts of 

 Asia, after having traversed a wide extent of ocean, pour a very heavy rainfall on these 

 coasts and outlying islands, thus very greatly lowering the specific gravity of the surface 

 during these months. 



The summer winds of Europe are determined by the high pressure of the Atlantic 

 in its relation to the low pressure systems of Asia and Africa at this time of the year. 

 On the coasts of Spain and North- West Africa the prevailing winds are northerly ; farther 

 to the north, on the coasts of France and the British Islands, south-westerly ; and on the 

 coasts of Norway westerly and north-westerly. The curving of the winds round the anti- 

 cyclonic region of the North Atlantic, from N.E. off the coast of Africa to E. and S.E., 

 as they near and pass the region of the West Indies, to S. and finally S.W. off the Eastern 

 States of America, has all-important bearings on the circulation of the waters of this 

 ocean. 



The centre of lowest pressure in North America is over the States about Utah, from 

 which pressure rises all round, but chiefly to the south-east and west. In accordance 

 with this arrangement of the pressure, the winds blow from the Gulf of Mexico home to 

 the coasts of the States as southerly winds. On the other hand, the winds on the coasts 

 of the Pacific States are N. and N.W. as far north as Vancouver, but over that island 

 and the coasts to northward they are S.W. 



