. A treatise on hygiene and public health . Fig. 16.—Sycamore water-supply. 25 feet deep, would hardly be called an artesian well, even if the tubepassed through an impervious stratum of clay. The general principle ofthe artesian wells is illustrated by the diagram. Fig. 17. The strata A B and CD are both impermeable to water, while K K ispermeable. The water which falls upon the outcrop of the perviousstratum KK tends to sink to the lowest portion of the stratum, andgradually to saturate with water the entire deposit. The water at the ON DRINKING-WATER AND PUBLIC WATER-SUPPLIES. 255 lowest pa
. A treatise on hygiene and public health . Fig. 16.—Sycamore water-supply. 25 feet deep, would hardly be called an artesian well, even if the tubepassed through an impervious stratum of clay. The general principle ofthe artesian wells is illustrated by the diagram. Fig. 17. The strata A B and CD are both impermeable to water, while K K ispermeable. The water which falls upon the outcrop of the perviousstratum KK tends to sink to the lowest portion of the stratum, andgradually to saturate with water the entire deposit. The water at the ON DRINKING-WATER AND PUBLIC WATER-SUPPLIES. 255 lowest part of the basin is under a very considerable hydrostatic pressure,and when an opening is made through the superincumbent strata, by bor-ing or otherwise, the water rises in the opening, and, in many cases, over-flows. The height to which the water will rise depends upon the heightof the line of saturation of the water-bearing stratum, at least in a. Fig. 17.—^Principle of artesian wells. measure; owing to friction, to the resistance of the air, and sometimes toleakage into the upper strata, the water will never rise to the height of itssource. It is not necessary that the permeable stratum in which the water isfound should be of the nature of gravel; many wells draw their supplyfrom rock strata. In the first place, all rock deposits are more or lessfissured and seamed, thus affording passage for water, and, in some rocks,especially of limestone, the solvent and erosive action of the water wearschannels and reservoirs. It is well known that limestone regions aboundin caves and often in underground streams. Independently of seams andfissures, however, large quantities of water may be stored in rock depositsby virtue of the porosity of the rocks themselves. Some rocks are socompact that they can absorb but little, while others may take into theirpores as much as one-third of their own bulk of water. This porosityis possessed not o
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Keywords: ., bookcentury1800, bookdecade1870, booksubjecthygiene, bookyear1879
