Joan Slonczewski's second novel, "A Door Into Ocean" (Arbor House, $17.95), portrays two neighboring worlds, Valedon and Shora. Shora is ocean-covered, its inhabitants parthenogenic human women whose society is built on genetic engineering and ecological balance. Valedon is autocratic and militaristic, and the plot revolves around its attempts first to exploit, then to conquer Shora. The novel is an impressive piece of world-building, with a varied cast of characters and a theme that seems a natural consequence of its premises. Slonczewski is not yet in a league with LeGuin, but she is clearly playing the same game - and playing it very well.
"The Memory of Whiteness" (Tor, $15.95) is Kim Stanley Robinson's third novel. The setting is the far future; thanks to the work of a brilliant physicist, Holywelkin, the human race has spread across the solar system. In his last years, the physicist devoted his efforts to music, creating a mechanical orchestra, the most perfect instrument known. The novel follows a young musician appointed Master of Holywelkin's orchestra as he undertakes a grand tour of the solar system. Robinson's future society is obsessed by music, and the novel effectively captures the thought processes of a composer. A murky conspiracy provides the plot momentum, but the real interest is in the remarkable play of esthetic and scientific ideas. Robinson's most ambitious novel to date, and a largely successful one.