CHAPTER LIV.
DIVING—THE FIRST DIVING-BELL—FIXED APPARATUS SUPPLIED WITH COMPRESSED AIR THE SUBMARINE HYDROSTAT—OPERATIONS AT HELL GATE—DIVING APPARATUS—SUBMARINE EXPLOSIONS—IMPROVED DIVING DRESSES—THEIR USE—WORK OF VARIOUS KINDS DONE WITH THEM—INSTANCES OF THIS—SEEKING THE TREASURE OF THE HUSSAR—SUNKEN SHIPS IN SEBASTOPOL—OPERATIONS IN MOBILE—THE DRY DOCK AT PENSACOLA BAY—THE BEAUTIES OF THE SUBMARINE WORLD—HABITS OF THE FISH—POSSIBLE DEPTH OF DESCENT.
Not only have men in modern times sought to extend their knowledge of the sea by dredging and sounding, but with the appliances of modern science they have attempted to plunge themselves into its depths, and provide the conditions there for not only remaining alive but for working. We have seen that the divers for coral and for pearls are enabled to remain under the surface only at the very outside two minutes, and that even this is such a strain upon the organs of the body that their lives are materially shortened by engaging in such work. Air is so indispensable to human life, that before any one can hope to remain any time under the water, some arrangement must be provided for supplying him with air.
DIVING-BELL.
The ancients, of course, knew that man was a breathing animal, they saw that each of themselves carried on this process constantly, but what they breathed they did not know, and they were equally ignorant of why they breathed. The discovery of what the air is belongs purely to modern times. About a century ago the astronomer Halley first proposed the use of the diving-bell, and went down in one he had built, to the depth of about fifty feet. The diving-bell was named from its original form, which was that of a bell, and this name is still retained, though the form of the vessel is changed. The supply of air is kept up by an air-pump worked above water. This is, however, a clumsy appliance in which the diver is limited only to that portion of the bottom on which the bell rests. Where there is either a strong current, or the bottom is very shelving, the diving-bell is embarrassing if not dangerous. In one case it is said that the diver was taken from the bell by a shark. Expert swimmers can dive from the outside, and, passing under the lip of the bell, rise suddenly inside of it, a feat which always surprises those who are in the bell. There is also sometimes danger that the bell may settle in the soft mud, and be held there by suction. Such a case once occurred in New York harbor, when a party had gone in the bell as a sort of pleasure excursion. The difficulty looked threatening, but one of the party proposed rocking the bell, and doing so the water was forced under, and the bell was lifted from the ooze.
FIXED APPARATUS SUPPLIED WITH COMPRESSED AIR.
As the workmen cannot leave the bell, this difficulty if possible is obviated by moving the bell. Frequently, however, submarine operations are to be carried on only in one spot, as in building bridges, when the foundations of the piers are to be laid, or in building breakwaters; laying the foundations of light-houses, or other similar work. In such cases, structures which in principle are the same as the diving-bell, are frequently employed. The one which was used to build the piers of the magnificent bridge over the Rhine, near Strasbourg is represented in the cut. Each of the piers of this bridge rests on a foundation composed of four large iron caissons, of great weight. Each caisson was open at its lower end. The upper part supported three shafts—a middle and two lateral ones. All three shafts arose above the water of the river. The middle shaft communicated with the open air, and the water rose in it to the level of the river. In this a dredging machine, driven by a steam-engine above, worked at the bottom of the river. The other two shafts were closed at the top. The workmen entering above the stream, closed their means of ingress air tight, and then air was forced in until the water was forced down, and out below, leaving the shafts free. The workmen then descended and filled the buckets of the dredging machine. When they wanted to ascend, they mounted to the upper part of the shafts; the air was let off, the water mounted in the shafts and they stepped into the open air.