The National Theatre screens a series of films each summer downtown. They’ve become so popular that, after last summer’s Hitchcock tribute, the theater began holding its mini-festivals year-round.

But there’s no better time to relax in an air-conditioned theater than during a heat wave, and this summer sees one of the best film programs yet. “Here’s Looking at You, Bogart: A Hollywood Legend” offers eight films starring the man many consider the greatest actor ever to grace the screen. The program started last Monday with “Casablanca.”