Ernst Chladni. Portrait of Ernst Florens Friedrich Chladni (1756-1827), German physicist and acoustics pioneer. He measured the speed of sound by filling organ pipes with different gases and noting the change in pitch. He used a violin bow to vibrate sheets of metal which were clamped in the middle then covered in sand. The sand formed a variety of different symmetrical patterns. These Chladni figures were due to the sand collecting in areas where the plate did not vibrate (nodes); these patterns allowed waveforms to be studied. Chladni also invented two musical instruments, the euphonium and clavicylinder.