Cartesian Diver
   The Cartesian Diver "consists of a glass cylinder nearly full of water, on the top of which a brass cap, provided with a piston, is hermetically fitted. In the liquid there is a little porcelain figure attached to a hollow glass ball a, which contains air and water, and floats on the surface. In the lower part of this ball there is a little hole by which water can enter or escape, according as the air in the interior is more of less compressed. The quantity of water in the globe is such that very little more is required, to make it sink. If the piston is slightly lowered, the air is compressed, and this pressure is transmitted to the water of the vessel, and the air in the bulb. The consequence is, that a small quantity of water penetrates into the bulb, which therefore becomes heavier and sinks. If the pressure is relieved, the air in the bulb expands, expels the excess of water which had entered it, and the apparatus being now lighter, rises to the surface. The experiment may also be made, by replacing the brass cap and piston by a cover of sheet india rubber, which is tightly tied over the mouth: when this is pressed by the hand the same effects are produced." Quote and cut from Ganot's Physics (William Wood and Co., New York, 1875), pg 89.

   This example is in the Garland Collection of Classical Physics Apparatus at Vanderbilt University. It is 59 cm tall.

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