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THEORY AN1J PRACTICE Ol* ENGINEERING.

Book II.

surface by boring, and that in many instances the supply will be sufficient, as in Artois inPrance, to turn the wheels of corn-mills.

In the terti iry basin of Perpignan and the chalk of Tours there are subterranean rivers,which have enormous upward pressure; the water rises near RousiUon in an artesian wellupwards of 40 feet above the surface, and M. Arago describes its force as sufficient to ele-vate a cannon ball placed over the mouth of the pipe.

M. Von Bruckmann sank an artesian well at Ileilbronn inWurtemberg, where the water was sufficiently warm to heat apaper manufactory ; similar wells are in use in Alsace , andnear Stutgardt.

In the Duchy of Modena are numerous artesian wells, as thereare also in America , Asia, and Africa : wherever impure wateris arrived at, it is necessary to continue the operation of boringuntil that desired is attained : the supply of water in these wellsis generally referred to the same principles as the play of an ar-tificial fountain, and their failure may be attributed to the rentsand faults which abound in rocks, or to the dip of beds, whichcarry the fluid in another direction.

The well bored at Sheerness was continued through 300 feetof clay, be'ow which was a bed of sand and pebbles, which whenpierced, the water immediately arose : in another situation thiswater was obtained at a depth of 328 feet below the surfaceclay.

In 1824 a well was bored at Fulham, 317 feet in depth, which,after traversing the tertiary stata, was continued through 67 feetof chalk, when the water arose, and was discharged at the rate of50 gallons per minute.

In the gardens of the Horticultural Society at Chiswick , theborings passed through 19 feet of gravel, 242 feet of clay andloam, ami 67 feet of chalk, after which the water arose to thesurface through the whole 329 feet. At Sion House, a shortdistance beyond, the boring was continued to the depth of 620feet, so as to enter the chalk, when the water rose in a considerablevolume, 4 feet above the surface.

In an artesian well sunk at Hammersmith water rose with aconsiderable force from a depth of 360 feet, and at rootinganother threw out sufficient to turn a water-wheel. By theborer it was found that, at St. Ouen in France , there werefive distinct sheets of water, from each of which a supply wasobtained; in the third, which was at a depth of 150 feet, wasa cavity in which the borer suddenly sank a foot or more, andthe water rose immediately in a considerable volume.

In the older geological formations, it is useless to attempt theconstruction of an artesian well, and among transition and se-condary formations, there is seldom an abundant supply of goodwater: in France , it is in the tertiary formations where theartesian wells succeed best, as that recently formed at Grcnelle.

In some instances shafts have been sunk increasing in diameter,lined with iron or masonry, and strengthened in their descent:these have passed through sheets of water down to a solidstratum, beneath which pure water has been found, and conveyedby an upright pipe to the surface.

Baring .—A well 6 feet in diameter is sunk to the depth of8 or 10 feet, and oue man above and two below are enabledto carry on the operation : over the well, is laid a horizontal polemade fast at one end, and the other is operated upon as theman above gives it a slight up and down motion, to suit theaction of the two below, it having a chain around it, connectedwith the cross-bar to which the boring instrument is attached.

This cross-bar or wooden handle passes through the socket of aniron shank, which has a ring at top, and a female screw atbottom ; to this all the successive boring instruments are fas-tened. A chisel is first attached to the screw, and the two work-men in the well press upon the cross-bar, and force it round like an auger at the sametime; this will continue to descend unless the ground is very hard or full of stones; whenit becomes necessary to drive it, and by changing its position occasionally, it is to revolve :after the first hole has been well opened, the chisel is changed for a cylindrical auger,

BOUING