Carl Sagan: A Life

In a superbly researched biography of one of the 20the century's most influential yet controversial scientists, Davidson (coauthor, Wrinkles in Time) leaves no doubt about where he feels his subject stands. ""What is a visionary?"" he asks in the closing chapter. ""Carl Sagan measured time in eons and space in light years; he maintained an interplanetary perspective."" Though many of Davidson's anecdotes echo those in William Poundstone's Carl Sagan: A Life in the Cosmos (reviewed above), he actively guides readers to conclusions, where Poundstone merely lays out the facts. Though not avoiding Sagan's many failings as a person, Davidson never allows his readers to lose sight of the grand visions, brilliant insights and brash speculations that inspired and educated Sagan's audiences. The book is at its strongest when it shows the inner Sagan through his most influential works: the Pulitzer Prize-winning Dragons of Eden; the Emmy and Peabody Award-winning television series Cosmos; his SF novel Contact; and his scientific publications about the runaway greenhouse effect on Venus, the windblown dust responsible for ""waves of darkening"" on Mars and the threat of ""nuclear winter"" after a limited nuclear war on earth. The volume is weakest when, instead of holding Sagan responsible for his sometimes arrogant behavior, it offers excuses from pop psychology. Though nonscientific readers may find Davidson's biography sufficient, naturally skeptical scientific readers may find its conclusions too firm for comfort. They should read Poundstone first, then turn to Davidson to complete the picture. (Sept.)