PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 177 



taken as unity, without introducing any notable errors into 

 calculations. The ranges of temperature are so consider- 

 able, however, and the depths of the bores frequently so 

 great, that it is worth while computing the amount by 

 which the potential would be raised by reason of the con- 

 trast between the cooler water near the intake, and the 

 warmer and lighter column in a bore several hundred miles 

 further out. 



Consider, therefore, a case in which water enters at 75° 

 F., and descends to a depth of 4,500 feet, by that means 

 acquiring a temperature of 200° F. Its density will gradu- 

 ally and nearly uniformly be reduced from 0*99732 to 0*9620, 

 and its mean density will therefore be 0*97966. From this 

 it can be shown that the static head of a bore 4,500 feet 

 will have been raised by temperature alone no less than 80 

 feet. The effect due to salinity may be neglected. 



The result will help to explain the rather high potentials 

 to be found over the western end of the Basin in South 

 Australia. Boring in the deep part of the Basin beyond 

 Bimerah will be looked forward to with interest in this 

 connection. 



The suggestion made by Dr. Jack and Oapt. Gipps that 

 tangible increases in pressure would be brought about by 

 actual expansion in volume due to rise in temperature 

 suffers from the same limitations as that derived through 

 rock pressure, as pointed out by Mr. G. H. Knibbs. 



(4) Hydraulic Pressure, — That the principal cause of 

 pressure is the greater altitude of the water-table on the 

 eastern margin of the Basin, cannot be denied in view of the 

 abundant and convincing data in support thereof, though 

 opinion may differ as to the way in which this head has 

 been developed. 



It should be pointed out at this juncture that in the 

 compilation of an isopotential map, one is confronted by a 

 number of difficulties. 



L— July 4, 1917. 



