A bubble may form in the bowl owing to the fact that some of the liquid has somehow escaped from the bowl. This is a bare occurrence and must be remedied by following the manufacturer’s instructions. In most compasses:
- Tilt the bowl until the “filter hole” comes upper most. This hole is provided on the side of the bowl.
- Unscrew the stud/screw provide.
- Top up with ethyl alcohol. If this is not available distilled water would be added.
- Screw the stud/screw back into place.
- Gently let the bowl return to upright.
In some modern compasses, small bubbles may be removed as follows;
- Invert the bowl gently. This would cause the bubble to enter a bubble trap provided for this purposes.
- Gently return the bowl to upright.
The bubble should have disappeared.
If the bubble is large. It would have to be removed as described in (1) to (5) above.