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.