19th Century Artificial Horizon

Interesting item from the late 19th century. Made by Chas C. Hutchinson - Boston. It was used in conjunction with a sextant to determine location. When in a position that does not include a view of the natural horizon, one would use the artificial horizon to get a fix on a star - directly and as a reflection off of the black glass. Small spirit levels are used to establish the artificial horizon on the surface of the black glass. Simply divide the angle in half to get the equivalent of a sextant reading.