A compass (when used for steering) is required to be damped so that the needle does not shakes rapidly and it is easier for the navigator to read off the compass. Therefore, In order to damp the compass a liquid is required to be filled up in compass bowl. This type of compass is called wet card compass. Now, this liquid is required to have the following properties -
1. Should not get evaporated in warm climates
2. Should not get frozen in cold climates
3. Should have Small coefficient of expansion
4. Should be clear
5. Should not discolor/damage the compass card
6. Low Specific gravity
7. Easily available

How to achieve this ?
This is achieved by the creating a mixture of distilled water and Ethyl Alcohol in the ratio of 2:1 respectively.
In warm climate, the distilled water prevents the mixture from evaporating (as the mixture is having higher ratio of distilled water)
In cold climate, the ethyl alcohol will prevent the mixture from freezing. The mixture has low coefficient of expansion (as mainly water is there) and the mixture is clear. Ethyl alcohol is easily available on ship.