When the undulatory current passed through the coil of this electromagnet, the disc vibrated, thereby creating sound waves in the air.
2.
On speaking into the mouthpiece, the iron diaphragm vibrated with the voice in the magnetic field of the bar-magnet pole, and thereby caused undulatory currents in the coil.
3.
The suspension also gave Bell time to amend his claims to avoid an interference with an earlier patent application of Gray's that mentioned changing the intensity of the electric current without breaking the circuit, which seemed to the examiner to be an " undulatory current " that Bell was claiming.
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