MUSHROOM DRILL.
The plan now undertaken is to undermine the whole bed of the river at this point, with a series of galleries connected by transverse galleries, leaving only so much rock standing in columns as shall insure stability to the roof above. When this work is completed, these submarine channels are to be charged with the requisite number of thousands of pounds of nitro-glycerine, and blown up with one grand explosion. This enormous work is now well under way, and is being rapidly pushed to completion. Work is carried on day and night, three sets of workmen being engaged in it, each working eight hours. The drilling has thus far been done chiefly by hand, and is very laborious. The workmen are chiefly Cornish miners, who alone can stand the severity of such mining. They are hardly ever dry while at work, and in the winter their clothes are frequently stiffened by ice. Preparations are however making to use machine drills operated by compressed air.
The operations of this mining under the channel of the East River have to be conducted with great care. Every inch of the way has to be critically explored. Seams of decomposed mica have been met, through which the water of the river ran as through a sieve. In one of the shafts such a seam was met, through which the water poured at the rate of six hundred gallons a minute, and could be stopped only by building a strong shield. The floor of the shaft follows a level about thirty feet below the low-water line. The roof follows of course the general contour of the reef, and to determine this, soundings of a special kind have to be taken. The bed of the stream is covered, except on the highest points of the reef, with a deposit of boulders, marl and organic matter from the sewers of New York, sometimes to the depth of ten or twelve feet. As the exact profile of the solid rock must be known before the miners can proceed, every sounding for determining this—and more than 15,000 have been already made—must be carefully done. The sounding apparatus consists of a float, or raft, supporting a machine like a guillotine or pile driver, by which a three-inch iron tube is driven through the overlying matter to the rock bed. The contents of the tube are then pumped out and an iron rod is used to determine the nature of the rock below. If it is a boulder, a dull thud is heard, and the rod does not rebound. Solid rock returns a sharp clink, and the rod springs back. The bearings of the tube are then taken by instruments from the shore, and the position of the rock calculated by a simple process.
READY TO GO DOWN.
Under the direction of General Newton, other submarine operations are also carried on in New York Harbor for the removal of the rocky and dangerous obstructions known as Diamond Reef, and Coentie's Reef, which lie in the busiest part of the harbor, directly in the track of the numerous ferry boats plying between New York and Brooklyn, and are not only troublesome, but dangerous, especially at low water. To perform this work, General Newton has had a special boat built, a scow, a low-lying, box-like craft, with a confusion of timbers, ropes, chains, and machinery surrounding a huge dome in the center. This vessel is very solidly built, and anchored so firmly that the waves strike against its sides as against a wharf. This strength is important for the work, and also to protect the machinery against the chance collision of the constantly passing vessels in the harbor. The general purpose of the scow is easily comprehended. Its object is to guard the drilling machinery while it is at work; to transport it when necessary, and to support the engines for working the drills. In the center of the scow is an octagonal well, thirty-two feet in diameter, in which is supported an iron-wrought dome for protecting the divers. At the top of the dome is a "telescope," twelve feet in diameter, with a rise and fall of six feet to adapt it to the various stages of the tides. When the dome is in working order, it stands clear of the scow, resting on self-adjusting legs, which adapt themselves to the inequalities of the reef. When the drills are working, the dome is down, out of sight, and the machinery, which at the first glance seems in disorder on the scow, is arranged in order, and is level with the deck. The engines which drive the drills are supported on moveable bridges, thrown back when the dome is up; and the drills work in stout iron tubes passing through the dome, one in the center, and the others arranged round it in a circle about twenty feet in diameter. The dome, when down, serves to protect the divers, so that at any time they can go down to regulate the working of the drills, or perform any other service. Without this protection, the divers could not keep their feet, so strong is the current on a rising or falling tide. The divers are protected by a diving suit; the air is furnished them by a pipe to the back of the helmet they wear, and is forced down by an air pump. When a set of holes are drilled, they are charged with nitro-glycerine, and simultaneously exploded by electricity.
This simple statement serves to show how much the modern methods of conducting such submarine operations are dependent upon the advance in chemistry of modern times. In fact, hardly a single appliance used in such operations, from the steam-engine which drives the drills, to the gutta-percha tubes, and the india rubber suits which enable the divers to descend below the water, but what are inventions or discoveries which belong entirely to modern times, and enable men to-day to perform operations which to the ancients would have really been impossible.
