A Cartesian diver. At the top of the jar is a rubber bulb filled with air. The figure inside the jar is made of glass and weighs less than an equal volume of water, so it will float. This image serves to illustrate the elasticity of air and the transference of pressure in all directions of the water.
International Correspondence Schools A Textbook on Mechanical and Electrical Engineering (Scranton, PA: International Textbook Company, 1897)