Ferris, who usually pokes around in outer space (Coming of Age in the Milky Way, The Red Shift, etc.), probes the inner kind as well in these amusing if far-fetched essays on the human mind, the search for extraterrestrial (and thus nonhuman) intelligence (SETI), and their intersection. For Ferris, SETI is a ""campaign of exploration,"" not a science, and all the more appealing for that; lying on the edge of knowledge, it proves fertile soil for the most extravagant musings. Where might a SETI signal come from, Ferris wonders? In a sort of computer-jock's ultimate wet dream, he imagines an ""interstellar network"" of automated space stations (""the most knowledgeable entity in the galaxy"") transmitting signals to similar networks in other galaxies. This Boschian vision leads to an exciting discussion of ""virtual reality,"" wherein computers simulate a foreign environment (say, the landscape of Mars) for stay-at-home explorers. Perhaps, Ferris posits, aliens are at this very moment sending us virtual-reality reproductions of their home planets. Ferris's ponderings also veer between the provocative and the preposterous. One bright essay analyzes star football quarterback Joe Montana as an uncanny example of a ""pre-motor cortex virtuoso,"" but another piece clumsily reduces mystical experience to a fuzzy ""confrontation"" with a ""program"" in the ""inner architecture"" of the brain. Other chapters, which read for the most part as independent pieces, consider comet strikes as a source of species extinction, near-death experience, apocalyptic prophecies, information theory, and the origin of laughter. Ferris's style remains as playful as ever (""we who came down from out of the forest seek to grow a forest of knowing among the stars""); too bad the thoughts seem sometimes stretched beyond their capacity to hold or convey the truth. The mind's sky indeed--but with clouds.