LETTEE IV. 



ON WAEM SPRINGS. 



The rocks, of which the outer crust of the earth 

 is made up, are everywhere more or less traversed 

 with clefts and hollows. These interstices form 

 natural basins which become filled with water, and 

 channels are established in which streams are 

 running often to great distances under-ground. 

 When such water-courses reach the surface at 

 spots, which lie below the level of the basin, 

 the water flows forth ; and thus Springs are formed. 

 However, springs may also be the discharges of 

 reservoirs that lie below them, if these latter 

 receive their supplies from places higher than the 

 level of the springs. In other words, if the 

 columns of liquid in the fissures are connected so 

 as to form a bent tube, filled with water, and 

 having one limb shorter than the other, then 

 the liquid must run out through any opening 

 in the shorter limb : this you may see any day 

 in the pipes of our waterworks. The velocity 

 of the flow depends on the difference of the height 

 of the two limbs of the bent tube, and augments 

 as this difference increases. 



It is this property of water which enables us 



