Signedunsigned
Inscribedwritten with pencil on both discs: 3
FunctionThis is a portable device that replaces the horizon when taking measurements with a sextant on land.
Instead of measuring angles from the height of a celestial body to the horizon as one would do on the ocean, what was done on land is to measure the angle between the celestial body and its reflection on a horizontal surface, which will give twice the angle to the horizon. One of the most used means as a horizontal reflecting surface was a mercury trough.
This model is highly portable and comes with a bottle of mercury with a protective wooden shell (5327b).
ProvenanceFrom the Department of Geology and Geography, Harvard University.