AETESIAN WELLS. 461 



Artesicm Wells. 



The existence of artesian wells depends upon that of subterra- 

 nean reservoirs and rivers, and the supply yielded by borings is 

 regulated by the abundance of such soui'ces. The waters of the 

 earth are, in many cases, derived from superficial currents which 



cited by Lombardini from the Memoires de V Academic des Sciences, t. ii., 1817. 

 Girard dug wells at distances of 3,200, 1,800, and 1,200 mi^tres from the Nile, 

 and after three months of low water in the river, found water in the most re- 

 mote well, at 4 m. 97, in the next at 4 m. 23, and in that nearest the bank at 3 m. 

 44 above the surface of the Nile. The fact that the water was highest in the 

 most distant well appears to show that it was derived from the inundation 

 and not, by lateral infiltration, from the river. But water is found beneath 

 the sands at points far above and beyond the reach of the inundations, and 

 can be accounted for only by subterranean percolation from the current of the 

 Nile at higher points of its course. At high flood, the hydrostatic pressure on 

 the banks, combined with capillary attraction, sends water to great horizontal 

 distances through the loose soil ; at low water the current is reversed, and the 

 moisture received from the river is partly returned, and may often be seen 

 oozing from the banks into the river. — Clot Bey, ApevQu sur I'Egypte, 1., 128. 



Laurent {Memoires sur le Sahara Oriental, pp. 8, 9), in speaking of a river 

 at El-Faid, "which, like all those of the desert, is, most of the time, without 

 water," observes, that many wells are dug in the bed of the river in the dry 

 season, and that the subterranean supply of water thus reached extends itself 

 laterally, at about the same level, at least a kilometre from the river, as water 

 is found by digging to the depth of twelve or fifteen metres at a village situ- 

 ated at that distance from the bank. 



Recent experiments, however, have shown that in the case of rivers flowing 

 through thickly peopled regions, and especially where the refuse from indus- 

 trial establishments is discharged into them, the finely comminuted material 

 received from sewers and factories sometimes clogs up the interstices between 

 the particles of sand and gravel which compose the bed and banks, and the 

 water is consequently confined to the channel and no longer diffuses itself later- 

 ally through the adjacent soil. This obstruction of course acts in both direc- 

 tions, according to circumstances. In one case, it prevents the escape of 

 river-water and tends to maintain a full flow of the current ; in another it in- 

 tercepts the supply the river might otherwise receive by infiltration from the 

 land, and thus tends to reduce the volume of the stream. In some instances, 

 pits have been sunk along the banks of large rivers and the water which filters 

 into them pumped up to supply aqueducts. This method often succeeds, but 

 where the bed of the stream has been rendered impervious by the discharge 

 of impurities into it, it can not be depended upon. 



The tubular wells generally known as the American wells furnish another 

 proof of the free diffusion and circulation of water through the soil. I do 

 not know the date of the first employment of these tubes in the United States, 

 but as early as 1861, the Chevalier Calandra used wooden tubes for this pur- 



