November 15, 1901.] 



SCIENCE. 



753 



openings, because resistance due to friction 

 along the walls and within the current is 

 very much less per unit circulation in large 

 than in small openings. While, therefore, 

 water enters the ground at innumei'able 

 small openings, as it goes down it more 

 and more seeks the larger openings. Once 

 found, it holds to them. The farther it 

 continues its journey, the greater the pro- 

 portion of the water which follows the 

 larger openings. But if this be true, the 

 water in its descending course is more 

 likely to be widely dispersed and in the 

 smaller openings ; and in its upward course 

 more likely to be concentrated and in the 

 larger openings. 



We can now follow the course of under- 

 ground water in detail, but in doing this it 

 is necessary to consider the elements of the 

 problem separately. It is only by passing 

 from a simple case to the very complex one 

 of nature that we can understand the latter. 

 Here is a chart (Fig. 3) which shows the 



imaginable case. In this illustration we 

 have represented the surface of the earth 

 and the level of ground water. By the level 

 of ground water is meant the depth at which 

 the water saturates the rocks — that is, where 

 the water remains at practically a permanent 

 level. Above this level the paths of cir- 

 culation are practically vertical ; below this 

 level the paths are curved. Of the water 

 which enters the slope of a hill and issues 

 in the adjacent valley, a portion flows 

 along the slope of the hill, a portion in 

 a less direct route, and a portion in a 

 very circuitous route. Below the level of 

 ground water all the openings in the rocks, 

 great and small, are filled with water. In 

 the case represented I have supposed that 

 all the water enters at a single point, A ; 

 and that all of it issues at a single point, B. 

 The curved lines represent the flowage of 

 the water through a homogeneous porous 

 medium. 



In the next chart (Fig. 4) I have sup- 

 posed water to enter at three points 



c e 



Fig. 3. 



surface of a slope, the level of ground water 

 and the flowage of water in the simplest 



Fig. 



and issue at one ; and I have supposed 

 the flowage from each point of entrance 



