Artesian Wells, small holes sunk in the earth, through which currents of water, struck at great depths, rise toward the surface, and sometimes flow over; so named from the province of Artois in France (Lat. Artesium), in which they have for a long time been in use. Water thus pressed up must have its source in some more elevated lands, and be confined in the strata of rock through which it has percolated; precisely as water is conveyed in pipes below the surface, and pressed up into buildings to a height nearly equal to that at which the pipes commence. Water finds its way down into the earth by flowing into the crevices and chasms of the rocks, and by percolating through the porous strata. In a region of limestone rocks it hollows out for itself its own bed, by dissolving the limestone, and even in this way produces great caves. When forced by the pressure behind, the water is pushed up through any apertures it meets and flows out as a spring or artesian well. There are three conditions essential to the successful boring of an artesian well: 1. A fountain head more elevated than the locality where the boring is to be undertaken. 2. A moderate downward dip of the strata toward the site of the well; a steep or high angle of inclination of dip is unfavorable, as the water is apt to flow away beyond the reach of the boring, which must needs pass at an acute angle through few layers of rock. 3. Alternations of porous and impervious strata beneath the surface soil.

It is sometimes the case that the head of water is at so high an elevation, that the column bursts forth from the ground as a fountain, throwing up a continual jet. The principle is precisely that of our artificial fountains. By raising the water above the surface in a pipe, and letting it flow over, convenient water power is obtained; artesian wells are applied to this purpose at many localities in France, the water they supply being found sufficient to run heavy machinery. From the great depth at which the currents of water are reached, their supplies may be regarded as permanent. A well at Aire in Artois, France, which was bored over a century ago, has since then flowed steadily, the water rising 11 ft. above the surface at the rate of 250 gallons a minute; and at Lillers (Pas-de-Calais) one well has flowed steadily since the year 1126. In the vicinity of London it is observed that the height to which the water rises diminishes as the number of wells is increased. In 1838 the supply of water from them was estimated at 6,000,000 gallons daily, and in 1851 at nearly double the amount, and the average annual fall of the height of the water is about 2 ft. But in cases of single wells, the supply of water or the height to which it rises is seldom known to vary.

From their depth, also, the water brought up is warmer than that found near the surface. This increase of temperature with the depth takes place at different rates in different places. At Paris, where the mean temperature at the surface is 51° F., the water of the artesian well of Grenelle is 82° from a depth of 1,797 ft., which is about 1° for every 58 ft. deep. At St. Louis, the temperature of the water at 1,515 ft. is 18.18° F. higher than the mean temperature at the surface, making the increase 1° for every 83.3. ft. descent. At Charleston, S. C, the temperature of the water at the surface is 68° F.; at 500 ft, it is 73.5°; at 1,000 ft., 84°; and at 1,106 ft,, 88°. The average rate of increase is about 1° for every 52 1/2 ft., as stated by Prof. Hume of the state military academy. The hot springs that flow out to the surface in many parts of the world are natural artesian wells rising from great depths. In Virginia these springs are found along the lines of great faults or breaks in the stratification of the rocks, by which formations usually separated by thousands of feet are brought into contact with each other. Warm waters obtained by artesian wells have been applied to useful purposes connected with manufacturing.

They are especially valuable where pure water of a uniformly warm temperature is required. In Wurtemberg large manufactories are warmed by the water being sent through .them in metallic pipes; a constant temperature of 47° is thus maintained when the temperature without is at zero. Hospitals and greenhouses are also kept warm in the same manner. - The strata of clays, sands, and limestones, which form the tertiary basins of London and Paris, are particularly well arranged for furnishing water by artesian wells. Covering areas of many square miles, the slope of the strata is toward the centre of the basin, and here, at the depth to which these reach, the waters must collect in large quantities. The strata, moreover, are not difficult to penetrate by boring. In these basins are concentrated the greatest number and the most expensive of these wells. The famous Grenelle well in the Paris basin was commenced in 1833, with the expectation of obtaining water at 1,200 or 1,500 ft., in the secondary greensand formation, which underlies the chalk, the uppermost member of this series.

For the first 50 ft. the bore was 12 in., which was then reduced to 9 in. for the next 1,050 ft,; a second reduction to 7 1/2 in. was made till the depth of 1,300 ft. was reached, where there was a final decrease to 6 in. At 1,500 ft. the government would have abandoned the enterprise but for the urgent appeals of M. Arago. It was continued till, on Feb. 26, 1841, at the depth of 1,797 ft., the boring rod suddenly penetrated the arch of rock over the subterranean waters, and fell 14 ft. In a few hours the water rose to the surface in an immense volume and with great violence, bringing up sand and mud. To check the supply a vertical pipe was raised many feet into the air, in which the water rises and flows over. The water is perfectly limpid, and flows at the rate of 500,000 gallons in 24 hours. It is used for warming the hospitals at Grenelle, as its temperature is uniformly 82° F. A well very similar to that at Grenelle, though of increased diameter, was begun at Passy, two miles distant, in September, 1854, and finished Sept. 24, 1861. The boring began at a height above the sea of 305.2 ft., and that at Grenelle at 121.3 ft.; the depth is 1,923 ft., and diameter within the tube 2.4 ft, The flow from this well began slowly, but on Sept. 27 had reached over 5,500,000 gallons per day.