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 272 NEW BOOKS. These and other practical hints are the most definite results of the author's investigations. He admits that it is not always possible to ascertain what faculties are possessed by a given individual ; because an action may be due to the exercise of any one of several faculties, and the lower faculties often " imitate " the higher, and produce the same results. But the thoughtful reader who tries in vain to discover what his powers are is told to console himself with the reflexion that even the author has not succeeded in making an inventory of his own. E. F. STEVENSON. Versuch einer philosophischen Selektionstheorie. Dr. JOHANNES UNBEHAUN. Gustav Fischer. This essay contains a " philosophical abstract theory of selection," and aims at a " purely deductive " method. It treats of the selection of everything, including inorganic objects (29, 96), works of art and writings (38, 130), species, cells, organs, tissues (103), molecules (104), parts of a state of consciousness, successive states of consciousness (113), instincts (118), firms and factories (128), languages (131), religions and philosophies (140), principles of thought and laws of research (142), and so on. The author points out that, for the possibility of a selection, we need " elements which sometimes come together into aggregates and again separate," and that these elements may be atoms and molecules, cells, organisms, persons, worlds and systems of worlds, or the separate ideas out of which a philosophical system is put together. He goes on to distinguish different kinds of selection. There is an outer selection between aggregates and an inner selection between parts of an aggregate ; each of these kinds may be either physical or psychical, and every case of selection is either with or without reference to special qualities. He finds that there are further a selection among the states of the same object and a selection among the relations between two or more objects, and develops these laws from a mathematical calculation of some complexity, in which three expressions occur. These are (1) the number of unit things concerned in a selection, (2) the time unit, and (3) the duration of each unit thing. Dr. Unbehaun is to be praised for having produced a work on natural selection, which is not a mere collection of unverifiable anecdotes. He has an undoubted knowledge of the literature of the subject from Malthus to Roux. He has seriously set himself to follow an orderly method, and to seize what is essential to the conception of natural selec- tion. In this work, the author has drawn many distinctions which are not familiar to the reader in this subject. And where all before was vaguely, but not the less really, statistical, Dr. Unbehaun openly develops his doctrines by means of a mathematical apparatus. On the other hand, it must be pointed out that the " elements which now come together and again separate " the " separate ideas out of which a philosophical system is put together" indeed, all such unrelated parts, or qualities, or states as doctrines of this kind must inevitably use exist neither in nature nor for thought, and the assumption which pro- duces them at the same time kills science. Either one state of con- sciousness is in some sense the same as that which follows it, or they are two separate things of which first one and then the other is selected. And the matter is not otherwise in the case of selection among animals and plants, and among their parts, their periods, and their qualities. Dr. Unbehaun's work is certainly as " abstract " and as " purely deductive " as he can have wished it to be. But these are not the marks of philosophical inquiry. G. SANDEMAN.