PROBLEMS OF THE ARTESIAN WATER SUPPLY OF AUSTRALIA. 109 



It would appear therefore that Professor Gregory, having 

 in view the great velocity of the water as it rushes from 

 the bores, has much overestimated its rate of flow in the 

 porous beds remote from the influence of the bores. 



In connection with this question it is interesting to note 

 that Professor Slichter has made a number of accurate 

 determinations of the rate of movement of groundwaters in 

 America. 1 He used for this purpose an ingenious apparatus 

 designed by himself. Several test wells are bored at short 

 distances apart along the approximate course of the flow. 

 The up-stream well is charged with a strong electrolyte, 

 such as sal ammoniac, and as the solution passes down 

 stream with the moving ground-water it forms a good 

 electrolytic conductor of electricity. Each of the down- 

 stream wells contains an electrode consisting of a nickeled 

 brass rod, and electrical connection is made between the 

 casings of all the test wells. As the electrolyte solution 

 moves in the direction of the down-stream well the electric 

 current between it and the up-stream well gradually rises, 

 mounting rapidly when the electrolyte begins to touch the 

 down-stream well. When the electrolyte finally reaches 

 and enters the down-stream well it forms a short circuit 

 between the casing of the well and the electrode, causing 

 an abrupt rise in the current, which is recorded by an 

 amperoraeter. By using three down-stream wells instead 

 of one, the direction of the flow, as well as its velocity can 

 be determined. 



The following are the results of 27 determinations made 

 by Professor Slichter, 2 at Long Island, New York : — 



1 C. S. Slichter, The Motions of Underground Waters, Water Supply 

 and Irrigation Papers of the U. S. Geol. Sur., No. 67, 1902. 

 a Ibid., p. 69. 



