After 51 years in the Soviet Union LÃ on Theremin started traveling , first visiting France in June 1989 and then the United States in 1991 , each time accompanied by his daughter Natalia , where he was reunited with Clara Rockmore who performed a number of concerts at this time . After 51 years in the Soviet Union Theremin started traveling , first visiting France in June 1989 and then the United States in 1991 , each time accompanied by his daughter Natalia .