Nathan Stubblefield Earth Cell battery
Stubblefield’s Earth Cell phone system
Electromagnetic induction works this way: Current passing through a primary coil of wire establishes a magnetic field of about 15 square feet. When a secondary coil is placed within the magnetic field, the primary coil induces current into the secondary one, even though the two aren’t touching. From his reading Stubblefield knew that the current could easily carry sound. He proved it one afternoon in 1892 to a teenager who lived next door.