44 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



IV. ARTESIAN WELLS. FOUNTAINS. 



The construction of artesian wells is also based on the principle 

 of the equal height of liquids in communicating vessels. It is true 

 that this condition is not the only one to be inquired into, and that 

 knowledge of the geological strata and of deep springs is also indis- 

 pensable. But we shall confine ourselves, in what we shall say 

 relating to this important scientific application, *to the point touching 

 the corresponding chapter of physics. 



Long before science had attained its present accuracy, fountains 

 or artesian wells existed. The ancient Egyptians and Chinese knew 

 how 7 to bore wells whence the water rose and came out in the form of 

 jets or flowing rivulets. In France, the ancient province of Artois 

 long ago possessed wells of this kind, and hence the origin of their 

 name. Theory accounts for their occurrence in this way : 



If we take a tube with two arms curved like a U, the water 

 poured into one of the branches runs into the other, and, as soon as 



equilibrium is established, the level of 

 the water is the same at a- and b, that 

 is, in both of them. Let us now sup- 

 pose that one of the branches is shorter 

 than the other and closed by a cock 

 that the longer branch is surmounted 

 by a reservoir full of water. If the 

 level c of the water in this exceeds the 

 distance by c d the level at the top of 

 the shortest arm, the liquid will exercise 

 a pressure on the bottom equivalent to 

 the weight of a column of water of 

 the height c d ; so that if by opening 



the cock this pressure be permitted to exert itself freely, it would 

 force out the liquid to a height which would be equal to c d, 

 if the resistance which friction against the sides of the tube and 

 the air displaced by the jet opposes to its movement be regarded ; we 

 must suppose also that the reservoir has such a capacity (if it be 

 not fed by a constant source) that its level does not itself vary 

 to any perceptible degree during the experiment. 



1 



FIG. 23. Principle of fountains and 

 artesian wells. 



