The senses of these words overlap, but historic should be used to refer to something that is renowned, influential, or history-making (the historic meeting of Livingstone and Stanley). Historical means "concerned with or contained in history" (a specialist in historical studies). Pronounce them "hi-STOR-ik" and "hi-STOR-ikal." Historically has five syllables: "hi-STOR-i-kal-ly." History should be pronounced "HIS-tuh-ri," not "HIS-try." See also a, an.
Dictionary of problem words and expressions. Harry Shaw. 1975.