This is a view of the back of it. The rest of the pics are at the same location. The stone is roughly level.
This is the bottom of it.
This is the front of it.
A detail from that pic. Note that the mercury reflects the angle.
A side view. Note that the angle is steeper.
From the same angle. It's reasonably obvious that the glass tube contains mercury and vacuum.
I saw this at the Roebling Museum near Trenton. It's near the old wire works which is now a superfund site. The steel mill was downtown and mostly abandoned. The museum is charming and Brother and I were the only visitors that day. The docent let me take it outside to get the pics.
It is made of cheap materials and crudely. No one has the faintest clue what it was used for or why it was made.
It is not a precision instrument and there are no markings of any kind.