About two-thirds through Asimov's bio-odyssey comes his thirteenth calculated figure: "The number of planets in our Galaxy on which a technological civilization is now in being equals 530,000." What has gone before has been an inexorable march of always scrutable logic leading him to conclude that life-advanced technological life--must be based on the carbon atom and the existence of "volatiles" (hydrogen, helium, neon, argon, water, methane, hydrogen sulfide); in short, on Earth-like conditions. To be sure, there may be some dolphin-like intelligences swimming in the oceans of some of the massive outer planets, but being streamlined, without appendages, they are unlikely to have the props of civilization. Elsewhere there may be bacteria or other lowly forms. The recent revelations of hydrocarbons and even more complex carbon molecules in interstellar dust seem only to confirm the universal chemistry of life. Given the probabilities, what next? How do we explore, send or receive signals--or should we? Here Asimov's rich knowledge of science fiction and fact lets him survey all the reasoned and wild-eyed speculations and dreams. And here his style takes on even more of a litany form of statement-and-response: a one-sentence paragraph supposing passage through a black hole, for example, is followed immediately by a rebuttal: "Yet. . . ." In the end Asimov feels that beginning with nearby space settlements may be the way, and by a stepping-stone approach over generations--reaching the limits of the solar system. If these settlements started coasting, picking up speed as they fly by the outer planets, they could leave the solar system forever, perhaps to find other "free-worlds." Short of seeding space, Asimov favors our feeble attempts to send messages--as in the Carl Sagas-Frank Drake records incorporated in the Pioneer 10 and 11 probes. At home, the possibility of building a large network of radio telescopes tuned to the most likely Sun-like stars might be sufficiently demanding technically and sufficiently informative to be worth the cost, not to mention providing a diversion from the arms race. And suppose a signal was picked up. Might it not provide "the crucial feather's weight that may swing the balance toward survival and away from destruction"? Asimovian optimism that's hard to resist.