Car-tē'sian or Cartesian devil1, a.
(kar-tē'zhan), a. Pertaining to the French philosopher Des Cartes, or to his philosophy. “The Cartesian argument for the reality of matter.” Sir H. Hamilton.
Cartesian devil, a contrivance to illustrate the effect of the compression or expansion of air in changing the specific gravity of bodies. It is a small glass figure, hollow, and sometimes provided with a hollow bulb on its head. This is to be partly filled with water, and placed in a tall vessel nearly full of water, and having a piece of caoutchouc secured tightly over the top. On pressing the caoutchouc, the air of the vessel will be compressed; this will compress that within the figure or bulb, so admitting more water by a small aperture, and causing the figure to sink. On removing the pressure, the air in the figure or bulb will expand, forcing out some of the water, and causing it to rise. Francis.