A chemical holiday-- and only professionals should go along. The humor comes off- preposterously enough for anyone- but the technical terms are forbidding despite explication, the research and scientific problems are recondite, and the basic theme calls for a highly developed scientific zaniness. The theme is the number- the precise astronomical number- of subatomic particles to be found.... well- wherever Asimov happens to launch his search. The passion for numbers extends to the number of periodicals, papers, conventions held by scientists; the number of possible variations in human nature; the number of steps it takes to walk from New York to Boston. But mostly it's the number of uranium atoms in the average acre of land- or astatine-215 if one mined all of North and South America, atom by atom, to a depth of ten miles. (Answer- about a trillion) More than one conundrum- for connoisseurs.