Of course he can only remain as long as the air which has been taken into his lungs will last him, and every one who tries to hold his breath knows that this cannot be for a long time. The diver generally closes his nostrils with a split stick, or something of the sort, to prevent the entrance of the water, and he is very careful to keep his mouth tightly shut. Water and air do not mix well in one’s lungs, and no man has ever yet invented a system of breathing water instead of air. At the depth to which the pearl diver descends, the pressure of the water causes a very unpleasant sensation in the ears, and before he has made many subaqueous journeys the drum of the ear is generally broken. The breakage of the ear-drum causes no serious injury beyond rendering the person who has undergone it hard of hearing, and instances have been known of divers becoming entirely deaf in consequence of the injury to their ears. [Illustration: PEARL DIVING IN THE EAST INDIES.] [Sidenote: IMPROVEMENTS IN DIVING.] [Sidenote: DIVING-BELLS.] As an improvement upon the primitive form of diving, the Diving-Bell was invented. It is called a bell on account of its shape, and not in consequence of any sonorous quality. It is constructed in the general shape of a bell, or an inverted tumbler; it is lowered, mouth downwards, into the water by means of ropes attached to a ship, a boat, or the arm of a derrick projecting over the water. Generally, however, it is let down from a ship’s side. The earliest diving-bells had no arrangement for supplying them with air. After the quantity within the bell was exhausted, the diver gave a signal by means of a rope, and the bell was drawn to the surface. At present the diving-bell has a flexible rubber tube attached to it, by which it is constantly supplied with fresh air, so that a diver may remain several hours under water without suffering for want of a pure atmosphere. The foul air is let out through a valve in the top of the bell, and is constantly rising in the shape of little bubbles. The pure air is forced down by means of a pump, which must be kept in steady operation. As long as this pump is at work, and the bubbles are rising from the bell, those above can be assured that everything is satisfactory; but let the bubbles cease to rise, and it is instantly known that something is going wrong.