the name applied to artificial springs, produced by boring a small hole through strata destitute of water, into lower beds in which water is percolating in considerable quantity. On making such perforation, the water often rises forcibly to the surface, and is conveyed to a convenient receptacle by a pipe introduced by the perforation into the strata affording the water. The first place in Europe where such artificial fountains were extensively formed was in the French province of Artois, anciently Artesium. But there is reason to believe that the art was long before practised by the Chinese, who are very expert in the formation of such wells. They are extensively used in the Milanese, in several parts of Germany, and have also been for several years employed in the south of England, on the coast of Lincolnshire, and more lately in the vicinity of London.
An artesian well was sunk at Sheerness in 1781, to the depth of 330 feet (Phil. Trans. 1784). It was carried through a thick bed of London clay, and water, which rose nearly to the surface, was found on reaching the subjacent sand-beds. Two of better construction were carried to the same depth through similar materials at Portsmouth docks in 1828 and 1829. The soil of the district on the coast of Lincoln between Lowth and the sea, rests on a thick bed of clay, which precludes the possibility of springs; but by penetrating through this, water was found in abundance in the chalk on which the clay reposed; and artesian wells there now afford a plentiful supply of this necessary element, that rises with such force through the pipes as to have obtained the local name of blow-wells.
The theory of artesian wells is founded on the fact that water derived from a higher level may percolate through certain strata, or pass in seams between them, and be prevented from reaching the surface by the superposition of other beds or strata impervious to water. In such circumstances a perforation through the latter allows the water, by hydrostatic pressure, to reach the surface; and it will overflow, or even gush out, with a force proportional to the difference of level of the different parts of the water-bearing strata, especially if the free course of the subterranean sheet of water be interrupted by what are termed faults in the strata, or the occurrence of veins of stony bodies intersecting them. Thus, in the diagram of a supposed section of a country, let PP represent a thick bed of plastic clay, A B C strata affording water, alternating with strata D E F, impervious to water, and let V represent a vein of trap rock traversing these strata, and producing a shift or fault; by sinking the pipes a b c into the strata A B C respectively, we shall obtain the water derived from the more elevated portions of these strata at such artesian fountains.
The same principles are applicable to the sinking of common wells. It has sometimes happened that a well has been lost in attempts to increase its flow by a deeper excavation. Thus, if the bottom of the well was a bed of clay resting on sand, a perforation made through that clay has occasionally lost all the water; because the stratum of clay had prevented the water from escaping to a lower level, and conducted it towards the surface. The direction of the strata, as well as their nature, are essential elements for the successful formation of either common or artesian wells; which last are of great consequence in campaign countries, where natural springs are less common.
Artesian wells have been also sunk for the purpose of obtaining warm water. It is well ascertained that in the interior of our earth there is a source of heat, which may be reached by deep artesian perforations, so as to bring warm water to the surface. Thus Von Bruckmann of Württemburg heated a paper manufactory at Heilbronn by water from a deep artesian well; and by the same means prevented the freezing of the water in winter round the wheels of mills. In the artesian well at Rochelle, at the depth of 370 feet, the water has a temperature 13° higher than that of the atmosphere. M. Arago was the chief promoter of the artesian well in the plain of Grenelle at Paris, which, at the depth of upwards of 1900 feet, affords water at 92° F. In the deepest artesian well yet made, that at Kissingen, the temperature of the water is also very considerable.
The instrument now used in making artesian perforations to great depths is not the old machine employed in boring for coal, &c., a series of iron rods screwed together, and forced down by repeated blows with a mallet. That was a costly and tedious operation; a Chinese instrument has lately been introduced with great effect. It consists of a heavy bar of cast iron, 6 feet long and 4 inches in diameter, armed at its lower end with a cutting chisel, surrounded by a cylindrical chamber, which, by means of simple valves, receives and retains the abraded portions of the rock. The instrument is suspended by a rope passing over a wheel. As it is wrought up and down, the torsion of the rope gives a circular movement to the bar of iron, sufficient to vary the position of the chisel at each stroke of the instrument; and when the chamber is full of the debris of the rock, it is drawn up and discharged. This mode of working has greatly diminished the labour and expense of such operations; and is applicable to many processes in mining, blasting in quarries, and the like.
An ingenious German engineer, M. Sellow, has by a similar instrument of greater size, succeeded in ventilating the mines at Saarbrück, by perforations 18 inches in diameter, and several hundred feet in depth.
The importance of artesian wells can scarcely be overestimated. They are capable of rendering districts now scantily supplied with or destitute of potable water, convenient domiciles for man; and under an enlightened government might render habitable no small portions of the arid wastes of Africa and Arabia. In the latter, recent observations show that there are abundant subterranean sources of water, and possibly a series of artesian wells might diminish the perils of the passage of the Great Sahara.—See Hericat de Thury, Considerations sur la cause du Jailissement des Eaux des Puitsforés, Paris, 1829; Von Bruckmann, Ueber Artesische Brunnen, Heilb. 1833; M. Arago, Notices Scientifiques.—Annuaire du Bur. des Long. pour Annes plus.
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