XLII. HYDRAULIC ASPECT OF THE ARTESIAN PROBLEM. 
number of minute tubes penetrating the artesian stratum, 
and distributed around the artesian well so as to form mano- 
meters, shewing the pressure heights. Then the surface 
defined by these heights, viz., the heights to which the 
water would rise in these tubes, would form the surface of 
pressure, and level contours would thereupon be curves of 
equal pressure. The system of curved lines orthogonally in- 
tersecting these would denote the lines of flow. (See Fig. 4.) 
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8. Complexity of probable actual conditions of problem.— 
It is by no means certain that the conditions are uniform 
over even very limited areas of the water-bearing stratum. 
If pierced by channels, as in some artesian regions, the 
resistance is locally greatly reduced, and the efflux from a 
well striking one of the channels would be large. Again 
if the stratum thins out, and is much consolidated at the 
point were the artesian bore penetrates it, the resistance 
is great and the efflux small. (See Fig. 4.) And yet again, 
if the water be in motion, a knowledge of its general trend, 
is necessary, not only to determine the relation between 
various wells but also as a guide to the study of local 
peculiarities, such for example as when a particular well 
gives a result in striking disagreement with expectations. 
Local variation of resistance will cause the local direction 
of motion of the water in the artesian stratum to differ 
