Boring

a method of drilling holes. In mining and in prospecting for oil three methods are employed. The simplest method is that of attaching various steel drilling instruments to the end of a cord and letting them fall by their own weight. This method has been long in use among the Chinese. In the second method the rope is replaced by a sectional rod which is raised from the hole whenever it is necessary to exchange a chisel for a scoop with which to remove the dust. The modern instrument, with which engineers bore holes from an inch and one-half to several inches in diameter, is the diamond drill. Pointed pieces of black diamond, harder than any other rock or metal, are set around one end of a steel tube. As this tube is rotated swiftly the diamonds cut an annular hole through the rock, permitting the tube to descend around a core. Water forced through the tube clears the cutting edge from dust and carries it up outside of the tube. As the instrument advances, the cylinder is lengthened by screwing on sections of iron tubing of the same diameter. The core is broken off and removed from time to time. In this way borings are made not infrequently to a depth of half a mile. Prospectors bore holes with diamond drills to ascertain whether a body of ore is worth working. Diamond drills, driven by small engines or electrical motors, are used extensively by miners and quarrymen in making ready for blasting. The superintendent or foreman of a mine not infrequently carries $20,000 worth of diamond points with which to replace those that have become dull. See Blasting