LONG BEFORE Mets outfielder Lastings Milledge rapped, baseball was inspiring songs like Let's Get the Umpire's Goat and Home Run Bill. (It begins: " Bill Johnson was a swatter on a Bush League nine.") The Baseball Songbook is a homely collection of 41 ditties written between 1867 and 1922. It includes sheet music, background stories, photos and a CD of author Jerry Silverman—who has also written a folk song encyclopedia—performing his selections. It's a sweet, simple book that hearkens to a sweeter, simpler time.