The device serves to demonstrate that in the elastic impact of an object on a smooth surface, the angle of incidence is equal to the angle of reflection.
At the base of the instrument there is a box containing a marble slab that can be tilted freely and is connected to a pointer that moves over a vertical semicircular board, to which an angular scale is attached.
When the ball is dropped vertically through the hole in the support, it strikes the marble at an angle determined by its inclination and rebounds in a direction that makes an equal angle with the slab.
Device on display.