On May 5, Milton Berle’s joke files—four cabinets holding thousands of 3x5 cards, indexed by subject—will be sold in Los Angeles. The comedian, who died in 2002, had a decades-long career in show biz, working in vaudeville, night clubs, films, radio, and finally and most famously on television. Berle’s live variety show “Texaco Star Theater” was the highest-rated program on TV in the late 1940s. The show was the first “appointment television”: Local businesses reported empty shops and restaurants during its airing, and cities experienced drops in water pressure in the five minutes after it was over, as everyone who...