On one of his most famous compositions, Scott "Mac" Davis sang, "I could just sit around making music all day long/As long as I'm making my music, ain't gonna do nobody no harm/And who knows, maybe I'll come up with a song..." The singer-songwriter-actor never had difficulty coming up with a song, including that memorable one. Davis, who died yesterday at the age of 78, recorded "I Believe in Music" on his second Columbia album in 1970, and the group Gallery took it up the charts in 1972.