The system now practiced in Great Britain, and on the Continent, is that in which the tools are attached to rods, consisting of a number of lengths, from ten to thirty feet long, joined by a separate collar, with a combined vertical and definite rotary motion, produced by a swivel joint in the upper length, or by suspending the rod to a “dog.” An ordinary well is first sunk to such a depth that the water below will rise, through the boring, into it. The object is to partly facilitate the object of boring, but chiefly to enable the pumps to be fixed without too great a length of suction. In deep wells, windlasses, driven by steam power, are used for operating the tool; the size of rod being, usually, 1¼ inch square; but for an eight foot boring, a 4½ inch square rod was used. To reduce the jarring and vibration, where borings are of considerable depth, the rods are hollow, in order to give same rigidity and resistance to torsion with less weight, and made buoyant, when working in water, by filling the rod with cork or light wood. A sliding joint, known as the “Oëuyenhausen joint,” is frequently used to bring the jarring only on that portion of the boring rod below. A shell pump is employed, in combination with the boring tool, for gathering the detritus, which obviates frequent raising of rod. Free-falling tools, guided by sliding joint, with catch or pall to raise same, are largely used. The weight of tool depends upon the depth and character of boring, that of the La Chapelle well being four tons. In the oil-well boring of Pennsylvania, the rope (with about 50 feet of iron bar, sliding jaws, sinking bar, flat drill and sand pump attached) are exclusively preferred. PRACTICAL EXAMPLES OF WELLS AS SOURCES OF SUPPLY ONLY. Where the surface soil and underlying drift possess sufficient porous qualities for absorption of a large portion of the rain-fall, together with the natural benefits of the impervious stratum beneath, having a proper axis of inclination favorable for conducting the infiltration of adjoining water-sheds, a large supply of water may be secured by the construction of dug wells for intercepting the subterraneous water. Fanning has computed the following available quantities, under favorable circumstances, for percolation, from one square mile of porous gathering area (the mean annual rain being assumed at forty inches depth). RATIO OF 1-12 OF VOLUME OF PERCOLATION NO. OF PERSONS IT MONTH. MEAN ANNUAL RAIN. IN DRY YEARS. WOULD SUPPLY AT FIVE INCHES. CUBIC FEET. CUBIC FEET DAILY.