    Sentence 1: What was it called when Tesla lit a  wireless gas-discharge lamp using a high-  frequency, high-voltage alternating current?    Sentence 2: At the Columbian Exposition, under a  banner announcing the "Tesla Polyphase System",  Tesla, demonstrated a series of electrical effects  previously performed throughout America and  Europe,:76 included using high-voltage, high-  frequency alternating current to light a wireless  gas-discharge lamp.:79 An observer noted: