AETESIAN WATER IN NEW SOUTH WALES. 287 



evaporation from an area of ocean only equal to that of Australia 

 were carried uniformly over that continent and were condensed 

 uniformly upon it there would be an annual rainfall everywhere 

 throughout Australia of about thirty-six inches, but as a matter 

 of fact there are large areas in Central Australia where the annual 

 rainfall does not exceed ten inches, and in places falls as low as 

 five inches, the latter being the average at Lake Eyre. This 

 deficiency of rainfall in Central Australia is due partly to want 

 of winds blowing inland from the ocean, but chiefly to the absence 

 of high ranges in the interior to serve as condensers. 



As regards want of suitable winds, Professor R. Tate, of Adelaide 

 University, remarks*: — " The aridity of Central Australia is a 

 consequence of its geographical position in reference to the region 

 of low barometric pressure, being the co-ordinate region of high 

 barometric pressure." This condition would obviously lead to the 

 prevalent winds in Central Australia blowing outward in a north- 

 westerly direction and would so check the advance inland of any 

 winds blowing from the Tropics. The south-east trade winds, it 

 is true, carry large quantities of moisture inland along the eastern 

 coast of Australia, but an undue share of this is condensed and 

 abstraced by the Cordillera, and after passing the latter owing to 

 the absence of any more high ground to keep the air cold the 

 moisture suspended in the form of clouds at the top of the Cordillera 

 is re-evaporated, as it moves further westward, simultaneously 

 with the re-heating of the wind as it descends to the level of the 

 western plains, over which it then sweeps as a dry wind. From 

 the Tropics also moisture is carried over a large portion of Aus- 

 tralia by the north-west return trade wind. The altitude however, 

 at which this wind blows, is so great that it is above the reach of 

 the condensing influence of any but the highest ground in Australia. 



These are a few of the causes, which conspire to make the rain- 

 fall in the central portion of Australia so much lower than it is 

 in other countries situated in similar latitudes in the Southern 



* Proc. Austr. Assoc. Adv. Science, Vol. i., p. 321. 



