The first Bell wall telephone, designed by Alexander Graham Bell in August 1877as a wall version of his "box" telephone. It contained a dynamic moving-iron driver that could be used as either a transmitter (microphone) or receiver (earphone) although is was mostly used as a transmitter with a separate earpiece receiver. It was constructed similarly to Bell's "box" telephone, with a horseshoe magnet with coils wound around the two poles near a sheet iron diaphragm. The difference was the pole pieces, diaphragm and mouthpiece horn were placed at right angles to the magnet. Caption: "The first commercial wall telephone"