The 100th birthdays of George and Ira Gershwin (in 1898 and 1896, respectively) are being celebrated around the world. The centennials are the perfect occasion to reflect on the brothers' rich legacy to American theater music. "The Man I Love," "Fascinating Rhythm," "Someone to Watch Over Me," "A Foggy Day"--together they wrote 700 songs and dozens of shows that defined an age and revolutionized the musical theater. Essential to any consideration of their achievement is Deena Rosenberg's Fascinating Rhythm, the only book to closely examine the brothers'extraordinary...