The band-wheel imparts motion in a third way, by means of an endless bull-rope turning the bull-wheels which wind or unwind the cable. The drilling •see consists generally of a bit four feet long, weighing 150 pounds; an auger stem about 40 feet long, and weighing 1,300 pounds; the jars, six feet or more long, weigh ing 300 pounds; the sinker bar, 16 feet long. weighing 600 pounds; and the rope socket of about 75 pounds on top. The total length of the string of tools is 00 feet. and when sus pended from the crown policy by means of the cable, one and seven-eighths inches in diameter, the tools swing inside the derrick, and when necessary can be stood up out of the way. When in use the tools are lowered into the bole by means of the bull-wheels, then are raised a few inches, and the rope is securely clamped to the temper-screw hanging to the end of the walking-beam, the rope above the point of at tachment being allowed to hang freely. By means of the temper-screw the tools can be gradually lowered as drilling progresses, the screw running down five feet. The bit or cut ting-tool is faced with steel, has an obtuse cut ting edge. The auger-stem is to give weight to the bit and efficiency to the blow. The jars consist of two long, flat links, faced on the in side with steel, playing into each other and per mitting a vertical movement of about nine inches. They divide the string of tools into two parts, acting in a degree independently of each other. Above the jars is the sinker-bar, whose purpose is to give efficiency to the up ward blow of the upper half of the jars. The jars are used mainly to loosen the tools if the lower part becomes wedged or stuck in the hole After drilling has progressed the length of a 'screw"— viz., five feet — the tools are hoisted out and water thrown in if the hole is dry. The sand-pump or bailer, a tube 16 feet or more long with a valve in the bottom, is then run in on the end of the sand-line, and when full of mud and water is drawn out and emptied, the operation being repeated until the hole is free from mud. Then a new bit, sharpened and of full width, is put on the end of the tools, tlicy are run in, and drilling proceeds as before. In some localities drilling is done by means of wooden rods instead of a rope. Where the rocks are soft or unconsolidated it is necessary that the well be lined with casing. This not only keeps the walls from falling in, but also, if properly set, keeps out surface or other waters. It is usual to drill the hole as rapidly as possible, and then slip the casing in, its diam eter being less than that of the drill. Some
times this cannot be done on account of the instability of the walls, and then it is necessary to adopt some modification, as, for instance, drilling ahead a short distance, and then driving the casing down. The latter is usually of wrought iron, put together by means of screw joints and collars, and capable of standing a pressure of from 1,000 to 3,000 pounds per square inch. In regard to the cost of boring wells, it is safe to assume that wells of 1,000 feet and under cost about $6 per foot; wells from 1,000 to 1,500 feet are relatively cheaper, being about from $4 to $5 per foot; and very deep wells are again relatively expensive be cause of the special machinery involved and cost over $6 per foot. An essential part of well-sinking equipment are several devices or •fishing tools' to be used in case a rope breaks of the drill becomes wedged in the hole.
Shallow wells are sometimes driven by ham mer blows and are known as driven or tubular wells. The tube so driven usually has a pointed end with perforation on the sides of the lower sections.
Well sinking has been carried on from pre historic times hut it was not until the 19th cen tury that improved methods and equipment made possible the boring of deep wells. In 1834-41 a well was sunk at Grenelle, near Paris, to a depth of 1,798 feet; not until 1850 at Kis singen. Bavaria, was this exceeded, when a salt spring was tapped at 1,878 feet. In 1855-57 a well 1.923 feet was sunk at Passy. near Paris.
The greatest depth reached by human agency n 7.570 feet in the Lake well, completed in 1919, at a point about eight miles southeast of Fair mont, W. Va. its mouth is about 1,300 feet above sea-level and it was bored in an unsuc cessful attempt to reach certain sands in which Fas and oil were expected. The next deepest is a well 7,386 feet deep on the Goff farm eight miles northeast of Clarksburg in northern West Virginia_ The third deepest is a well at Czu chow. Germany, which is 7,348 feet deep. The fourth in order is the Geary well 20 miles south west of Pittsburgh, Pa., 7,248 feet deep. The following are more than 5,000 feet deep.
There are many from 3,000 to 5,000 feet deep. The deepest mine In the world is shaft three of the Tamarack Copper Mine, Houghton, Mich., 5.330 feet, and other copper mines in Lake Supe rior region are from 4.000 to 5.000 feet deep. Consult lster, C., 'Well-Boring for Water, Brine and Oil' (2d ed., revised and enlarged, London 1911).