PROFESSOR GRAY'S TELEPHONE. .1Ar Pig. IPROFESSOR GRAY'S TELEPHONE IN NEW YORK. 2PROFESSOR GRAY'S TELEPHONE IN PHILADELPHIA., scientific american, 1877-04-28

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PROFESSOR GRAY'S TELEPHONE. .1Ar Pig. IPROFESSOR GRAY'S TELEPHONE IN NEW YORK. 2PROFESSOR GRAY'S TELEPHONE IN PHILADELPHIA., scientific american, 1877-04-28

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