Undated draft of patent 231,704. Receiver is same as previous except it's placed in tertiary circuit "to keep the apparatus free from earth currents which cause alteratios in the volume of sound owing to the marvellous delicacy of the apparatus." Claims method of connecting buttons to circuit; rubber transmitter cover; use of primary & secondary coils in transmitter; receiver's palladium-tipped pressure arm; call battery; receiver. [Receiver tertiary circuit not in claims of this draft.]

Edison, Thomas Alva

Serrell, Lemuel Wright

1879-07-17

1870-1879

Patent Application

Acoustic telegraphy

NS79AAG1

NS79

[NS79AAG1], Patent Application, Thomas Alva Edison, July 17th, 1879

162:714

Thomas Edison National Historical Park

Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University