George M Phelps US Patent Electric Speaking Telephones 214,840 4-29-1879 Phelps Transmitter and Arm

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George M Phelps US Patent Electric Speaking Telephones 214,840 4-29-1879 Phelps Transmitter and Arm

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George M Phelps US Patent Electric Speaking Telephones 214,840 4-29-1879 Phelps Transmitter and Arm.pdf