2203. Wells are vertical excavations in the earth; always of such a depth as to penetrate a porous stratum charged with water, and mostly as much deeper as to form a reservoir in this stratum or in that beneath it. A well otherwise excavated is a mere tank for the water which may ooze into it from the surface strata. The form of the well is generally circular, and to prevent the crumbling down or falling in of the sides, this circle is lined with timber, masonry, or zones of metal. The earthy materials being thus pressed on equally in every point of this circle, are kept in equilibrium. When the well is not very deep, and in firm ground, this casing is built from the bottom to the top, after the excavation is finished; but when the soil is loose, the excavation deep, or its diameter considerable, it is built on the top in zones, sometimes separated by horizontal sections of thin oak boards, which, with proper management, sink down as the excavation proceeds. There are various other modes, which those who follow this department of architecture are sufficiently conversant with. The height to which the water rises in the well depends on the height of the strata which supply the water; occasionally it rises to the surface, but generally not within a considerable distance. In this case it is raised by buckets and levers, by buckets and hand-machines placed over the well, or by buckets raised by horse-machines.
