The assiduous Mr. Asimov, in addition to his science fiction chillies, juveniles, and popular science books, admits to live count 'em five other books of science essays previously featured in The Magazine of Fantasy and Science Fiction, and this latest again contains a beaker full of science tidbits, restating of present controversies, flights of fancy, autobiographical anecdotes, and numerical parlor games. Of varying degrees of difficulty (Asimov's first chapter concerning the Law of Conservatism presupposes some knowledge of mathematical and chemical interactions) this smattering of educated guess-and-by-golly's reminds one of the amusing and informative dinner talk of a loquacious scientist. The more adventurous will enjoy Asimov's explication of a "time" theory, concerning cosmogony, with divisions of the "cosmic egg" moving backwards and forwards in time, therefore unable to interact. Speculation un-pure perhaps, un-simple, but entertaining and sure to please Asimov's following. More of the same from Asimov's busy grotto.