Original: It was originally scored for a chamber group of flute\/piccolo , clarinet ( B flat and C ) , two pianos , glass harmonica , xylophone , two violins , viola , cello and double bass , but is usually performed today with a full orchestra of strings , and with a glockenspiel substituting for the rare glass harmonica .
Simplified: Today it is often performed with a full orchestra of strings , and with a glockenspiel instead of a glass harmonica , which is an unusual instrument .