Pisis
2nd Lieutenant
OK, here's the answer:
Greetings! The name of the object is "liquid compass".
There are many types from many manufacturers. In some modifications, it is used even todays. This type probably comes from a pre-WW2 Czechoslovak aircraft. NO WAY it was ever used in a German one! In some of them, they used a liquid compass marked FK 38.
Cheers,
Šilhánek