The title, though accurate, does not catch the flavor of this latest Asimov--which reveals his fascination with limits and man's "restless desire" to push beyond. As preamble, Asimov reviews human physical limitations: horizons defined by human eyes, legs, and so on. Then, in true Baconian scientific spirit, he celebrates the experiments, methods, and measurements that have extended human horizons in space, time, matter, and energy. The result is a bird's-eye view of history and invention, science and industry. Spatial horizons make up the bulk of the work, what with Asimov discoursing on the ancient Mediterranean world, Marco Polo, the age of exploration, the conquest of the poles, the eras of ballooning, flight, and space--with asides on oceanography and mountaineering. Time horizons have to do with the ever-finer splicings of time (did you know that "second" simply means the second division of an hour?) and the clever timepieces that made precision possible--inevitably leading to questions of the age of the earth, the universe, and living creatures, and the conundrums of relativity and time travel. The horizons of matter are graded from the mini to the mighty in living and non-living matter, with sections on weight, mass, density, and pressure. In horizons of energy, the subjects are heat, temperature, and luminosity; predictably, Asimov raises cosmological questions on the fate of the universe, and describes the blackness of black holes and the brightness of quasars. He's said many of these things before, of course; but they are condensed and tied together here in highly satisfactory fashion, with the earthy wit (black holes as "cosmic subways") and the usual scattering of Guinness record-type tidbits. Vintage Asimov that will please fans--and also a lively introduction to science for teens or pre-teens.