"Cole Porter gave various accounts of how he came to write "Night and Day." He once said the music was influenced by an Islamic call to worship he'd heard while traveling in Morocco. Porter also said he began the tune on a Saturday night at New York's Ritz-Carlton Hotel, and wrote the lyrics the next day while lying on a beach in Newport, Rhode Island. He wrote it specifically for Fred Astaire. "Night and Day" is the song with which a besotted Astaire finally captures the stubborn heart of Claire Luce on Broadway and Ginger Rogers in the Hollywood version, "The Gay Divorcee." He sings, they dance, oh, did they ever, and she melts. In the film, the producers replaced all of the original Cole Porter tunes except for "Night and Day." It begins with one of the most unusual verses in popular song, pulsing, monotonous, insistent."
Music From NPR in 2000: