GENERAL CONSIDERATION. 5 



reservoirs " and " imperfect reservoirs." In a "perfect reservoir" 

 the water has no outlet at a lower level than the artificial one pro- 

 vided by the well. In an "imperfect reservoir" the water possesses 

 a natural escape at a lower altitude than the well. Yet there may 

 still be a tendency to rise owing to the resistance opposed by fric- 

 tion along the underground channel leading to the natural outlet. 

 Such a condition is represented in Mr. Medlicott's experiments 

 illustrated in the Report already referred to. The following diagram 

 which has been several times reproduced from Daniell's Text-book 

 of the Principles of Physics in works dealing with the present sub- 

 ject, gives a better idea of the facts than any description :— 



Some of the artesian reservoirs that have given the most 

 brilliant results are of the nature of " imperfect reservoirs." The 

 Dakota sandstone, a cretaceous rock in North America, may be 

 quoted as an example. 



In the report just referred to, Mr. Medlicott also pointed out 

 that artesian conditions are generally very different from the ex- 

 ceptionally favourable conditions that hold good in the typical 



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