Let's see. . . if you took all the books written by Isaac Asimov and placed them end to end, the line would reach from Broadway and Fourteenth Street to the orbit of maybe Jupiter. . . . Anyway, this is one of the best. Asimov organizes with determination rather than elegance. Oddly, the most obvious aspect of this subject (the history of Arctic and Antarctic exploration) is the most routinely handled. It's the maze of interconnected physical facts about the Poles that presents the greatest difficulties, and here Asimov is in his element. The climate of the Poles? It can't be understood without reference to the terrestrial shape, orbit, rotation, inclination of axis, atmosphere, and oceans. The Pole Star? It hasn't been the Pole Star forever, because of the precession of the equinoxes. Polar ice and glaciers? The Ice Ages? That brings in the atmosphere again and the problem of how its water content is affected by geographical features, causing different precipitation patterns--hence different glacial histories--at the North and South Poles. The aurora? That involves the earth's chemical composition, the still unsolved riddle of its magnetism, and the interaction of the solar wind with the ionosphere. Asimov is painstaking, clear, thorough (though it must be noted that at the end of a long discussion of everything imaginable about the aurora, he still hasn't gotten around to why it's visible) and as infectiously enthusiastic as a small child.