Demonstration sounding tubes. Late 19th century

Demonstration sounding tubes probably r. Koenig, late 19th century. These 4 lacquered brass tubes are mounted on a mahogany base. Each has a brass plunger piston which, when withdrawn rappidly, produces a sound whose frequency depends on the length of the standing column. Each tube has his own wavelength marks: ut3 – mi3 – sol3 – ut5. Measurements 37 x 15 x 37 cm.