If life is often a matter of split seconds -- the train door that closes in your face, the chance encounter with the love of your life, the near-collision with an oncoming car -- then the universe is about to bestow upon us a generous gift: the leap second. Saturday, at exactly 6 p.m. Chicago time, one second will be added to our official record of time -- Coordinated Universal Time, kept by a series of atomic clocks, housed in environmentally sealed vaults in about 80 timekeeping labs around the world and certified by the International Bureau of Weights and...