DIVING BELL

An apparatus by means of which persons are let down and enabled to remain under water, and execute various operations; such as levelling or clearing the bottoms of harbours, preparing a foundation for buildings, bringing up sunken materials, . The principle of she diving bell depends on the impenetrability of atmospheric air,and may be illustrated by a very familiar experiment. Bring the edge of an inverted tumbler, or any close ve el, to the surface of water, and, keeping the month horizontal, pre it down in the water. It will be seen that, though some portion of water ascends into the tumbler, the greater part of the space remains empty, or only filled with air; and any object placed in this space, though surrounded on all sides with water, would remain perfectly dry. In fact, the quantity of air remains the same, but is compre ed into a smaller volume, in proportion to the depth to which it is made to descend. Now, if we conceive a ve el of wood or iron, sufficiently capacious to hold several men, to be suspended by a chain, and lowri\l by means of weights attached to it to any moderate depth under water, it is evident that they may remain there for a considerable time, and perform any operation;.h:it could be executed on land in the same confined space. Hie machine, however, as thus described, is liable to two 358 r [s. 372]