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Artesian Wells are most available, and of the greatest use, in low and level districts where water cannot be obtained from superficial springs, or by ordinary wells of moderate depth. Fountains of this kind are known by the name of Blow wells, on the Eastern coast of Lincolnshire, in the low district covered by clay between the Wolds of Chalk near Louth, and the Sea-shore. These districts were without any springs, until it was discovered that by boring through this clay to the subjacent Chalk, a fountain might be obtained, which would flow incessantly to the height of several feet above the surface.
In the King's well at Sheerness sunk in 1781 through the London clay, into sandy strata of the Plastic clay formation, to the depth of 330 feet, the water rushed up violently from the bottom, and rose within eight feet of the surface. See Phil. Trans. 1784.) In the years 1828 and 1829 two more perfect Artesian wells were sunk nearly to the same depth in the Dock yards at Portsmouth and Gosport.
Wells of this kind have now become frequent in the neighbourhood of London, where perpetual Fountains are in some places obtained by deep perforations through the London
both strata is thus brought to the surface by one Bore Hole of sufficient size to contain a double pipe, viz. a smaller pipe included within a larger one, with an interval between them for the passage of water; thus, the smaller pipe b brings up the water of the lower stratum B, to the highest level of the fountain b″, whilst the larger pipe a brings up the water from stratum A to the lower level a: both these streams are employed to supply the Canal-basin at St. Ouen, above the level of the Seine. Should the lower stratum B contain pure water, and that in the upper stratum A be tainted, the pure water might by this apparatus be brought to the surface through the impure, without contact or contamination.
In common cases of Artesian wells, where a single pipe alone is used, if the Boring penetrates a bed containing impure water; it is continued deeper until it arrives at another stratum containing pure water; the bottom of the pipe being plunged into this pure water, it ascends within it, and is conducted to the surface through whatever impurities may exist in the superior strata. The impure water, through which the boring may pass in its descent, being excluded by the pipe from mixing with the pure water ascending from below.
