for the year 1881. xix 



laws depending upon the rotation of the earth itself, and, 

 therefore, upon position on the earth's surface, upon the 

 distribution of land and water, and upon the seasons. It 

 may perhaps be stated that, generally speaking, the normal 

 direction of the wind over the earth is westerly, for we 

 find in the Southern Hemisphere below 40 deg., where there 

 is but little land to interfere with any normal current, it 

 blows strongly and regularly from the west at all seasons of 

 the year, except when temporarily disturbed by cyclonic 

 movements. Our atmosphere may be likened to a great 

 stream moving eastwards, meeting with islands, continents, 

 and shoals, and affected largely by powerful thermal in- 

 fluences, which, as it sweeps along, gives rise to innumerable 

 deflections, eddies, and whirlpools, and so divert the general 

 movement as to produce currents in all directions. We can 

 witness these in miniature in almost any steadily flowing 

 river. The little whirlpools with their depressed centres 

 represent the cyclonic movements of our atmosphere in 

 some places, and the higher portions in their neighbourhood 

 the anticy clonic areas which disturb the normal flow of the 

 earth's atmosphere. The barometer always indicates the 

 pressure to be less in the cyclonic than in anticy clonic 

 areas, and the question of how these vertical movements 

 arise, what governs their progression, their dimensions, 

 duration, and the paths they follow, is now the most 

 interesting problem in meteorology. 



The climatic conditions of a continent as brought about 

 or affected by these general laws of pressure and movement 

 of our atmosphere may be perhaps illustrated by taking- 

 Australia in the summer season as an example. The 

 Australian colonies are now all connected by telegraph, and 

 from most of them telegrams, giving the state of the 

 weather, temperature, height of barometer, direction and force 

 of wind at nine a.m. every clay are received in Melbourne ; 

 if, now, these are plotted upon a chart of Australia, we have 

 presented a rough kind of contoured survey of the 



