476 ARTESIAN WELLS. 
Artesian Wells. 
The existence of artesian wells depends upon that of sub- 
terranean reservoirs and rivers, and the supply yielded by 
borings is regulated by the abundance of such sources. The 
waters of the earth are, in many cases, derived from superficial 
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 Nile. At high 
flood, the hydrostatic pressure on the banks, combined with capillary attrac- 
tion, 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. 
—CuLor Bry, Apercu sur ? Egypte, i., 128. 
Laurent (Mémoires 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 kilométre from the river, as water 
is found by digging to the depth of twelve or fifteen métres at a village situat- 
ed 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 
laterally through the adjacent soil. This obstruction of course acts in both 
directions, 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 
intercepts 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 cannot 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. Ido 
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- 
