DIVING DIVING BELL 155 the air which is forced into it to be so diffused as to be breathed without inconvenience. The breastplate permits a free expansion of the lungs and sufficient motion to avoid constraint of the muscles. To the lower part of it is at- tached an India-rubber dress, having a body, legs, and arms ; shoes are fitted on, and the whole is impervious to water. The central window of the helmet can be readily removed without removing the helmet. Leaden weights are attached to the waist and soles of the shoes to enable the diver easily to maintain an erect position when standing or walking upon the bottom. A pump, shown in fig. 2, which is usually supplied with three cylinders, forces air through a flexible but strong India-rubber tube into an opening in the back of the helmet, which leads through a flat channel to the fron- tal portion, where it is delivered against the glass windows, thus serving not only to supply the lungs of the diver, but to clear the moisture from the inner surface of the windows. The air finds its exit also at the back of the helmet. The air from the pump is free to pass down the waist and into the legs, between the person and the dress, and is delivered with sufficient force to overcome slightly the hydrostatic pressure. Fig. 2 represents the diver in the act of spreading a large bucket of hydraulic concrete upon the bed of a harbor, preparatory to laying blocks for the foundations of a pier. A signal rope communicates with an attendant on a boat which contains the air pump. The signals of the diver are communicated verbally by the attendant to a director stationed upon the derrick by which the buckets of concrete or blocks of be"ton are moved into position, and by him bells are rung which enable the atten- FIG. 2. The Diver spreading Concrete. dant at the engine to execute the necessary movements. In 1856 Mr. E. P. Harrington of Westfield, N. Y., recovered the iron safe of the steamer Atlantic, sunk four years previously in Lake Erie in about 170 ft. of water. The safe itself was at the depth of 157 ft. He used a common flexible India-rubber armor, unpro- tected with metal, and supplied with air sent down from a pump through a tube of f -inch bore, composed of nine alternate layers of canvas and rubber, with a copper wire coiled inside to prevent collapse. He also wore shoes of lead, and carried weights of lead amounting in all to 248 Ibs. His first descent was on June 19, and the 18th and last was on the 22d, when he succeeded in attaching a line to the safe, which was in a state room on the upper deck, and it was hauled up. The time of his remain- ing below increased from one minute at the first descent to 11 minutes at the last. At the depth of 50 to 70 ft. all light disappeared. He suffered from extreme chilliness ; his strength too, he thought, was diminished nine tenths. The pressure sometimes caused a violent rush of blood to the head, and the appearance of bright flashes like electrical sparks. DIVING BELL, a hollow inverted vessel, in which persons may descend to considerable depths, fresh air being forced down from above to supply the amount required for breathing, and under which upon the bottom they may work to prepare foundations, or to secure ar- ticles of value. The principle of the diving bell is seen in pressing any vessel like a tum- bler mouth downward into water. The air within the vessel prevents the water from rising and filling it, but it is made to occupy less space as the pressure is increased with the in- creasing depth of the water. If the vessel were forced down to the depth of 33 ft., the
