Augustin Santi - Artificial Horizon
Augustin Santi was a scientific instrument maker and optician between 1830 to 1862 and was based in Marseille, France. 
Information on the net for Santi is hard to find.
This item is a very rare 19th century Artificial Horizon. There is an onyx surface housed in a tribrach arrangement and the set includes a bubble level.

Artificial Horizon - when the horizon of the visible landscape is obscured by darkness or inclement weather such as fog or other causes making it difficult to measure the altitude of a celestial body an instrument known as an "Artificial Horizon" is used to serve as an alternative to obtain accurate altitude readings on land.

Please see the Santi theodolite in my collection as well.

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The " Treatise on Mathematical Instruments" by F.W.Simms ( 1844 ), scanned by the University of California, Los Angeles, describes in detail on pages 63 and 64 the theory and practise of both this artificial horizon and the Elliott artificial horizon in my collection.