CHT163517 Harmonic Hand, from \'L\'Harmonie Universelle\' by Marin Mersenne (1588-1648), 1636 (engraving) (b/w photo) by French School, (17th century); Private Collection; (add.info.: studied the acoustics of vibrating strings and organ pipes; measured the speed of sound; wrote on music, maths, optics and philosophy;); 穢 Archives Charmet; French, out of copyright.