Fig. 122. 



136 WELLS'S NATURAL PHILOSOPHY. 



bore do^-n through the upper stratum, as at b, until we reach the stratum 



containing the water, the water will rise in the excavation to a certain height, 



proportional to the height or level of the water accumulated in the reser- 



vok a a from which it tlows.* 



.„^ . ^ . 305. The rain which falls upon the surface of the earth 



What IS the on- . , , i ^i , , , 



gin of springs ? smks Qownward through the sandy and porous soil, un- 



tQ a bed of clay or rock, through which the water can not 

 penetrate, is reached. Here it accumulates, or running along the surface 

 of tlie impervious stratum, bursts out in some lower situation, or at some point 

 ■where the impervious bed or stratum comes to the suiface in consequence of a 



valley, or some depression. 

 Such a flow of water consti- 

 tutes a spring. Suppose o, 

 Fig. 122, to be a gravel hill, 

 and b a stratum of clay or 

 rock, impervious to water. 

 The fluid percolating through 

 the gravel would reach the 

 impervious stratum, along which it would nm until it found an outlet at c, at 

 the foot of the hill, where a spring would be formed. 



„^ , 306. If there are no irregularities in the surface, so situated 



Aivhv does water " . . 



coik-ct in an or- as to allow a spring to burst forth, or ii a sprmg issues out 



dinary well ? ^t some point of the porous earth considerably above the sur- 

 face of the clay, or rock, upon which at some depth all such earth rests, the 

 water soaking downward will not aU be drained off, but will accumulate, and 

 rise among the particles of soil, as it would among shot, or bullets, in a water- 

 tight vessel If a hole, or pit, be dug into such earth, reaching below the 

 level of the water accumulated in it, it will soon be filled up with water to 

 this level, and ^•iU constitute a well The reason why some wells are deeper 

 than others, is, that the distance of the imper^nous stratum of clay below the 

 surface is different in different localities. 



„ . , 307. All wells and springs, therefore, are merely the rain- 



Frora what , . , , 



Bonrce do all water which has sunk into the earth, appearing again, and 



MTrinsrs^d'^rive gradually accumulating, or escaping at a lower level. 



their water? 308. The property of liquids to assume a horizontal sur- 



"WTiat is a ^^<^^ '^^ practically taken advantage of in ascertaining whether 



Water, or ^ surface is perfectlv horizontal, or level, and is accomplished 

 Spirit Level? , „ . ' , „ -rrr „ 



by means of an instrument known as the Water or 



'Spirit Level." This consists of a small glass tube, b c, Fig. 123, filled 



with spirit, or water, except a small space occupied with air, and called 



• In the great Artesian wells of Grenelle, near Paris, and of Kissinpen, in Bavaria, the 

 water risfs from depths of 1,900 .ind 1.900 feet to a considerable height above the surfaca 

 of the earth. The well of P.iris is capable of snpplyinr wnter at the rate of 14 millions 

 of gallons per day. The region of country in which this water fell, from the curvature 

 of the layers, or strata of material through which the excavation was made, must hara 

 been distant two hundred miles or more. 



