What is the purpose of filling magnetic compass bowls with liquid?

The purpose of filling magnetic compass bowls with liquid is to dampen oscillation of the float. When a magnetic compass is in use, it is sensitive to movement and vibrations, which can cause the compass needle to oscillate. By filling the bowl with liquid, the movement of the needle is slowed down due to the viscous properties of the liquid. This damping effect stabilizes the reading, allowing for more accurate navigation, especially when the aircraft is encountering turbulence or changes in flight attitude. The liquid reduces the tendency of the compass needle to bounce around, providing pilots with a clearer and steadier indication of heading.