Pascal, a french scientist determined the law of transmission of fluid pressure which is known as Pascal’s law. This law states that the pressure applied at any point of a confined fluid is transmitted with undiminished magnitude in all directions throughout the fluid and acts normally on the surface in contact with the fluid.
Demonstration of Pascal’s Law:
Take a rubber ball and fill it with water. The mouth tightly. Take a pin and make fine holes at many points on its surface. If the ball is squeezed, it is seen that jets of water come out in the direction normal to the surface of the ball. Observe that the jets are all of the same speed and that this speed depends on the squeezing force applied. This shows that the applied pressure is transmitted equally in all directions throughout the liquid and acts normally at every point on the surface.
In the above demonstration, the effect of gravity has been ignored. This is justified only if the height h of the rubber ball is sufficiently small so that the pressure hρg at its bottom is negligible compared to the pressure due to the externally applied squeeze.