The whys and wherefores of our inner clocks, zestfully presented by journalist and novelist Orlock (The Goddess Letters, 1987). You say hello, and I say goodbye. So it goes, for people's body clocks are rarely in sync--and, according to Orlock, these internal timekeepers control just about everything we think, feel, or do. Chronobiology has uncovered over a hundred biological rhythms so far, with more on the way. They fall into three categories: ultradian (short--e.g., the firing of neurons); circadian (24-hour--e.g., the wake-sleep cycle); and infradian (long--e.g., the menstrual cycle or--the longest of them all--the life/death cycle). Orlock's jaunty tour of this fledgling science includes plenty of ethology, including Darwin's studies of biorhythms in plants and earthworms. The focus, however, is on humans--who appear to be a lot like puppets tugged by chemical strings. Migraines, calorie intake, alacrity of thought--all bow before internal cycles. Some facts amaze: when asleep, we ordinarily ``breathe through one nostril for three hours, with the tissue in the other nostril slightly engorged, then we switch''; more sobering is Orlock's discussion of the millions of Americans who suffer from Seasonal Affective Disorder--serious depression brought on by winter. To battle the cycle blues, Orlock proffers plenty of advice: If you want to lose weight, eat in the morning; for best sex, wait until October; to cure jet lag, splash yourself with sunbeams. How to tell inner time--and how to beat the clock. Fun.