ARTESIAN WELLS, deep wells bored through impervious rock strata to a porous water bearing rock stratum whence the water flows to the surface and is discharged from the bore. The principal condition of an artesian well is a pervious stratum protected above and below by a water-tight bed. These layers come to the surface in some ele vated region where they get their rain flow, then pitch downward to a consider able depth and then rise again, thus forming a great basin which retains the water. Rain water and surface water fill the porous stratum to the brim. If it be tapped any, the water will rise in the bore and be discharged as long as the supply equals the de mand. The whole Mississippi valley is ideally adapted for wells of this kind. The Chinese and Egyptians were early acquainted with artesian wells. The oldest known in Europe is at Lillers, in Artois (hence the name artesian), and was sunk in 1126. In 1836, the first artesian well was dug in the eastern Sahara and at a depth of nearly 200 feet struck water which poured forth 4,500 liters a minute. In 1860 there were 50 wells, averaging 735 liters a minute. In the province of Constantine alone there are more than 150. The re sult is proving beneficial not only to the country materially, but also to the character and habits of its nomadic Arab inhabitants. Several tribes have already settled down around these wells, and, forming thus the centers of settle ments, have constructed villages, planted date palms, and entirely renounced their previous wandering existence. The earliest exploration for artesian water in Colorado was at Kit Carson Station on the Kansas Pacific railroad. It was sunk to a depth of 1,300 feet without obtaining water. In 1879, a well was drilled for petroleum at South Pueblo, in the Arkansas valley. At a depth of 1,180 feet a flow of mineral water (82°) was struck yielding 160,000 gallons per 24 hours. Subsequently thousands of
wells were dug in Colorado. It was found that Denver was underlaid by a body of artesian water. The American Desert, which includes one-fifth of the total area of the United States, has deep artesian wells which were bored for the purpose of irrigation, and which have transformed the whole region.
The most famous artesian well, per haps, is that of Grenelle, near Paris, which was bored in 1833-1841, and whose water is brought from the Gault at a depth of 1,798 feet. It yields 516% gallons of water per minute.
Artesian wells have supplied a por tion of the data upon which the internal temperature of the earth has been cal culated. Thus the Grenelle well has a temperature of 81° F., while the mean temperature of the air in the cellar of the Paris observatory is only 53°. MM. Arago and Walferdin observed the tem perature as the work proceeded, and found that there was a gradual and regular increase downward. Walferdin also made a series of very accurate and careful observations on the temperature of two borings at Creuzot, within a mile of each other, commencing at a height of 1,030 feet above the sea, and going down to a depth, the one of 2,678 feet, the other about 1,900 feet. The results, after every possible precaution had been taken to insure correctness, gave a rise of 1° F. for every 55 feet down to a depth of 1,800 feet, beyond which the rise was more rapid, being 1° for every 44 feet of descent; but at Fort Randall the temperature at 80° increased at the rate of 1° every 17% feet. It was once supposed that water from artesian wells was purer than from ordinary wells; but it is found to be a mistake. The lower the water goes, the more impreg nated it is with saline and other matter.