compasses have Mineral Oil filled Needle Housings, with steel needles that pivot on a sapphire bearing
The light mineral oil is there to damp the needle (stop the needle swinging too loosely) and it has to withstand freezing (because compasses are used in cold places).
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The predominate liquid used inside a filament transformer is mercury. Mercury is used to keep the transformer cool when under heavy use. Mercury is a cheap and long lasting liquid.
The prismatic compass is a type of compass use for survering a land.
M9 paper is used to detect liquid chemical agents such as blister or nerve agents.
A compass is used by various people in different fields to know their location and destination. The most common professions that use a compass are pilots, ship captains and also geographers.
In a DC circuit yes. The compass detects the magnetic field around the wire. Reverse the DC current and the compass will swing 180 degrees from the position is was in.