A law of physics which states that a confined fluid transmits externally applied pressure uniformly in all directions. Blaise Pascal, using the mercury-column barometer of Evangelista Torricelli, demonstrated the decrease in atmospheric pressure with increasing height and determined that atmospheric force at a point exerted equal pressure in all directions. More exactly, in a static fluid, force is transmitted at the velocity of sound throughout the fluid. The force acts normal to any surface. This natural phenomenon is the basis of the pneumatic tire, balloon, hydraulic jack, and related devices.