Every reader understands the general principle involved in the construction of the diving-bell. Invert a tumbler in a deep vessel of water, and the liquid will only ascend to a certain height inside, however far down you place the glass. Insert a tube in a hole drilled in your tumbler, and blow downwards, and the water recedes still lower. This is what happens when the air is pumped down into the modern diving-bell. In descending in a diving-bell and remaining under water you will feel a slight inconvenience in breathing, and perhaps a tingling in the ears; this comes, not from scarcity of air, but from the fact that the atmosphere of the interior of the bell is really _denser_ than it is outside; the air, forced downwards by the powerful air-pump, is pressed _upwards_ by the water. Readers may remember that Robert Fulton and his friends remained under water in his submarine boat for over two hours, the air in that case being supplied from a large globe containing highly condensed air, which was allowed to escape as required. The foul air passed off from tubes in bubbles to the surface.
[Illustration: A DIVER AT WORK (WITH SUBMARINE LAMP).]
As early as the year 1663 an Englishman named William Phipps, the son of a blacksmith, invented a plan for recovering from the bottom of the sea the treasures out of a Spanish vessel which had sunk on the coast of Hispaniola. Charles II. lent him a ship and all that was necessary for his enterprise, but the matter did not turn out successfully, and William Phipps fell into a state of the greatest poverty. Notwithstanding this nothing could discourage his ardour, and to set himself afloat again he opened a subscription list in England, of which the Duke of Albemarle was one of the subscribers. In 1667 Phipps embarked in a ship of 200 tons burden, having undertaken beforehand to divide the profits between the twenty shareholders who represented the associated capital. At first starting his search proved altogether unavailing, and he was just beginning to despair, when he fell in with the golden vein. The fortunate diver returned to England with £200,000; £20,000 he kept for himself, and no less than £90,000 came to the share of the Duke of Albemarle. Phipps was knighted by the king, and became the founder of the noble house of Mulgrave, which has played no inconsiderable part in the affairs of the United Kingdom.