For a guy who is a nonprofit environmental education organization founder, United Nations Environment Programme goodwill ambassador, and a former analyst for the U.S. Coast Guard Oil Pollution Act, John Francis spent a good amount of his earlier years keeping his mouth shut. Prior to racking up that list of achievements, a younger Francis decided in 1973 that the best way to promote social change was to, uh, take a 17-year-long vow of silence and walk across America. It wasn’t until Earth Day 1990 that Francis spoke again—and, by that time, he had plenty to say, much of which he detailed in his 2005 memoir, Planetwalker: How to Change Your World One Step at a Time. Part road trip, part meditative journey, Francis’ book is as inspirational as it is enlightening; along the way, he earned a Ph.D. in land management, looked down the barrel of a racist deputy sheriff’s gun, and silently contemplated issues of environmentalism and world peace—all of which would provide him with more than enough material with which to talk the talk once he had finished walking the walk. Francis discusses and signs copies of his work at 7:30 p.m. at National Geographic Museum at Explorers Hall, Grosvenor Auditorium, 1600 M St. NW. $18. (202) 857-7700.