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Show New Harmonica Typo A "chemical harmonica," twin gas flames In glass sounding bells flanked by rotating mirrors, was one of the physical exhibits of A Century of Progress exposition at Chicago. The sounding bells are arranged as organ pipes with a metal stop at the bottom bot-tom opening to permit the entrance of air which causes vibrations, giving giv-ing forth the tune. Pitch is controlled con-trolled by the length of the bell. The vibrations are visible only through the use of mirrors. |