Gravity, that awesome, ubiquitous presence, is too often reduced here to a springboard for launching a handful of fevered conjectures. ""Gravity schmavity,"" as the ad folk behind Wonderbra might have it. But the force never relents: Unhook that undergarment, and gravity goes to work. It tucks you into your chair, shapes your tears, keeps the universe from splintering outward. The strength of attraction is inversely proportional to the square of the distance between the objects--and, as the author notes, ""down is the only direction."" Lanza (The Cocktail, 1995, etc.) starts out pleasingly enough, detailing the history of elevators (early ones were thought of as thrill rides for the strong-hearted) and the influence of gravity on the crafting of furniture, such as the Eames Chair, with its ""base so slim it seemed to lift derrieres from the ground."" He ponders Salvador Dalfs dystopia as a deep-seated gravity aversion; tackles everyday kitchen vexations, such as how toast, knocked off a counter, will ""always rotate at an angular velocity of 180 degrees and hence, never has a desirable landing"" (namely, it will indeed always land buttered side down). But Lanza is also happy to delve willy-nilly into suspect terrain: ""The roilercoaster's fusion of manly mechanical with the matronly organic gives it an androgynous edge."" How's that? He concocts a forced pas-de-deux of distant cousins General Norman Schwarzkopf and Anton Schwarzkopf, a designer of roller coasters, and their ""separate but parallel gravity wars."" Consider this a paradigm of antigravity: a brief incandescence of entertainment followed by notions so light they melt--vapidly, forgettably--into thin air.