The Master Violet Ray’s basic construction was invented before the 20th century by Nikola Tesla, who introduced his first prototypes at the World's Columbian Exposition in 1893. Most of the antique violet rays in the US were produced before the Depression, it was a medical appliance used to discharge in electrotherapy. Their construction usually featured a disruptive discharge coil with an interrupter to apply a high voltage, high frequency, low current to the human body for therapeutic purposes