What is "lutheal"

The luthéal is a kind of hybrid piano which extended the "register" possibilities of a piano by producing cimbalon-like sounds in some registers, exploiting harmonics of the strings when pulling other register-stops, and also some registers making other objects, which were lowered just above the strings, resound. The instrument became obsolete partly because most of its mechanics were too sensitive, needing constant adjustment. The only pieces in the general repertoire to feature the luthéal are L'enfant et les sortilèges (1920–25) and Tzigane (1924) by Maurice Ravel.