Last Saturday morning at Spreckels Lake in Golden Gate Park I was mesmerized watching a Tai Chi class performing a graceful series of moves on a sandy peninsula that juts into the water. The synchronized movements, reflected in the slightly wind-rufflled water, seemed to flow in widening ripples into the surrounding morning, radiating calm. This class, led by Master Bill Chin and other experienced practitioners, is offered free of charge every Saturday and Sunday from 8:30 to 10:00 a.m. in this idyllic setting. Anyone can join; beginners are encouraged to participate and learn by following along. Advanced participants wearing red wristbands are interspersed among those less practiced. The class ended while I was still sketching, but I’m planning to get there in time to join in next weekend.