The Seven Day Circle: The History and Meaning of the Week, Eviatar Zerubavel (Free Press/Macmillan). "Why was the seven-day week invented? Why are TV programs aired weekly instead of every four or nine days? Why are suicide rates higher on Monday and lower each weekend?" In this "refreshing" look at why we need such obviously artificial time frames, Zerubavel "suggests that culture, not nature, dictates how" we measure time.