American electrical engineer Lee De Forest, inventor of the Audion (triode) vacuum tube, and one of the first AM radio transmitters, from around 1920. The Audion made practical amplitude modulation (AM or audio) transmitters possible, and was responsible for the rise of radio broadcasting around 1920. The box on the left is the transmitter, the one on the right is a receiver. The Audion vacuum tubes are visible mounted on the front of the device. De Forest is speaking into a telephone-type carbon microphone, which was connected directly in the antenna lead to modulate the radio carrier. The caption read: ""Dr. De Forest trying out one of his recent inventions, a portable wireless telephone operated entirely by current from a lamp socket."" Most early radios operated from batteries; this one had an internal rectifier to allow it to operate from the AC wall current.