Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

TRIPOD DRILL (PNEUMATIC) WORKED UNDER WATER BY DIVER. It has been found in some cases that if the rock is of a precipitous nature, the best method is to commence drilling a row of holes parallel to the edge, and at a distance from it equal to the depth of the holes ; the holes being driven to about 3ft. below the required level. After blasting out these holes a fresh series are drilled parallel'to the former ones, or to the face left by the blasts^ and these also blasted out—a third line—and so on, progressing regularly across the rock, continually blasting it off in parallel blocks extending downward a little below the depth required. I he advantage of this mode of operating is that it enables the blasts to act laterally, in which direction they are more powerful, and the rock is left after each series of blasts with a nearly vertical side or face^ in which the presence of seams can be detected and the character of the strata observed^ so that the most favourable positions for the next blasts to produce the greatest effect can be selected. Sometimes the craters following the strata run under or leave an overhanging face, in which case a large charge usually has the effect of throwing off the overhanging portion, and often dislodges large masses of rock. With a rock drill of good construction, it is possible to do as much work in a few hours as would take several days with hand tools. The Diver can easily be taught the use of the drill on land, and when conversant with its working, he will not find the slightest difficulty in carrying out the boring operations under water. The working vessel (some engineers prefer to work the drill from a raft, or a barge, with a well in the centre, having water-tight compartments) having been moored over the rock, the Diver descends and selects the exact position for the blast, and then signals to have the drill and stand lowered to him. This being done, he fixes the drill in position by means of its adjustable legs, and then signals to commence supplying the drill with com- pressed air. Sometimes the drill works uninterruptedly till the hole is drilled to the required depth ; at other times its working requires the attendance of the Diver, either in replacing drill-heads broken by contact with hard crystals, or in regulating the turn or “hoist” of the drill, or in clearing the holes of cuttings, or “spooning out,” as it is termed, and rectifying the direction of the drill by adjusting the legs or guys. In a rapid current the stoppage of the drill for the purpose of “spooning out ” the holes becomes unnecessary, as the motion of the drill works up the powdered cuttings to the mouth of the hole, whence they are sucked out and carried off by the current. As soon as the hole is drilled to the required depth the drill is stopped, and, after an examination of the hole and clearing away any cuttings remaining in the bottom, the Diver telephones or signals for the charge of explosive (which has previously been carefully pre- pared with detonators hermetically closed, and with insulated wires extending to, but not yet connected with, the electric battery on deck) to be lowered to him, and he inserts it in the drill hole, carefully pressing it to the bottom with a rod. The tamping*if any is used, is then inserted above the cartridge (the charges should be of such size as to pass into the bore holes easily— i.e., the diameter of the bore hole should be in. to £in. larger in diameter than the diameter of the cartridge). The Diver then ascends, and the working vessel is hauled to a safe distance. The wires are then attached to the battery, a few turns given to the handle, and the operator makes the contact, when a shock, followed instantly by a second shock and the upheaval of the water, announces the explosion of the charges. I he working vessel is then brought back to the position as before, and the same opera- tion repeated. . In cases where the rock is naturally “ fissured,” it is not necessary to bore holes, as the cievices or fissures themselves form very good receptacles for the placing of the explosive charges, s a 1 ule, under these circumstances it is difficult to apply tamping in such a way that the full efficiency is obtained from the explosive. In such a case a waterproof bag filled with dynamite would be the best form of charge to use, as it would shape itself to the inequalities of the rock. * If a tamping rod be used, it is important that it be cylindrical throughout—not pointed at the end. IOI