What is the purpose of filling the capsule of a Silva compass with liquid?

Filling the capsule of a Silva compass with liquid serves the important function of dampening the compass needle. When a compass needle moves freely, it can oscillate or swing excessively due to minor movements or vibrations. By adding liquid to the capsule, the needle's motion is slowed down, allowing for more stable and accurate readings. The liquid creates resistance against the needle's movement, which helps it to settle more quickly and point more steadily towards magnetic north. This feature is particularly useful in dynamic environments, where steady readings are critical for navigation.

While visibility, friction reduction, and corrosion prevention are relevant considerations for compass functionality, the primary and specific purpose of the liquid filling is to enhance the accuracy and usability of the compass by dampening the needle's movement.