The bane of this science, as every one knows, has been its theorizing, and its want of careful inductive reasoning from facts. The classifications in it have been endless, varying almost with the fancies of each new student; while every prominent follower of it has had some pet hypothesis, to which he desired to suit his facts. Whether the _a priori_ theory were of modern miraculous origin or of gradual development, of unity or of diversity of parentage, of permanent and absolute divisions of races or of a community of blood, it has equally forced the author to twist his facts. Perhaps the basest of all uses to which theory has been put in this science was in a well-known American work, where facts and fancies in Ethnology were industriously woven together to form another withe about the limbs of the wretched African slave. Waiz has reasoned slowly and carefully from facts, considering in his view all possible hypotheses,--even, for instance, the development-theory of Darwin,--and has formed his own conclusion on scientific data, or has wisely avowed that no conclusion is possible. The classification to which he is forced is that which all profound investigators are approaching,--that of language interpreted by history. He is compelled to believe that no physiological evidences of race can be considered as at all equal to the evidences from language. At the same time, he is ready to admit that even this classification is imperfect, as from the nature of the case it must be; for the source of the confusion lies in the very unity of mankind. He rejects _in toto_ Professor Agassiz's "realm-theory," as inconsistent with facts. The hybrid-question, as put by Messrs. Gliddon and Nott, meets with a searching and careful investigation, with the conclusion that nothing in facts yet ascertained proves any want of vitality or power of propagation in mulattoes or in crosses of any human races. The unity of origin and the vast antiquity of mankind are the two important conclusions drawn. His second volume is entirely devoted to the negro races, and is the most valuable treatise yet written on that topic. The whole work is mainly directed towards _Naturvölker_, or "Peoples in a State of Nature," and therefore cannot be recommended for translation, as a general text-book on the science of Ethnology,--a book which is now exceedingly needed in all our higher schools and colleges; but as a general treatise, with many new and important facts, scientifically treated, it can be most highly commended to the general scholar. _Il Politecnico. Repertorio Mensile di Studi applicati alia Prosperità e Coltura Sociale._ Milano, 1860. New York: Charles B. Norton, Agent for Libraries, 596, Broadway.