Description:
The instrument is framed in wood and supported by two rectangular feet. The above wave pattern is made of several narrow wooden strips that can move up. Below is a solid wooden wave pattern that is inserted from the right. Its handle is made of a thin piece of brass. Two more, with different patterns, are stored behind the instrument on wooden brackets.
Once a wave pattern has been inserted, the handle at the back is lifted up. The solid wave pattern, when moved up by this lifting motion, pushes up the narrow strips of wood composing the above pattern. The new pattern resulting from this push is the interference pattern of the two waves.
On top of the frame, behind, "four" and "4" have been handwritten. Similarly for one of the solid wave pattern. It was probably shop-built at Harvard University.