Why is liquid necessary in a magnetic compass bowl?

Liquid is necessary in a magnetic compass bowl primarily to dampen the oscillations of the float. In a magnetic compass, the float is connected to a magnet that aligns itself with the Earth's magnetic field. When the aircraft moves or experiences turbulence, the float can swing rapidly, which can make the compass reading unstable. The liquid helps to slow down these movements, allowing the needle to settle accurately and provide a reliable reading.

The use of fluid in the compass bowl is integral to its functionality, as it effectively minimizes erratic behavior under varying conditions. Without the liquid, the float would be more susceptible to quick movements, resulting in a compass that could give false or confusing readings. This damping effect is crucial for pilot navigation, ensuring that the compass reliably reflects the aircraft's heading.