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238 CRITICAL NOTICES : these terms appear to do, exclusively to intellectual development. The distinction between primary and secondary cannot be scien- tifically defined ; it can only be experienced. The term which best designates the secondary phenomenon is " Vorstellung". Any- thing which we have ever once been conscious of can be afterwards reproduced. " The reproduction of feelings is an indubitable fact of the mental life." Eepresentations of feelings, however, are not feelings, nor are memories of volitions acts of will. Feelings an^ acts of will are primary phenomena at whatever stage of develop- ment they occur. The " tertiary " phenomena are distinguished from the secondary as fusions and condensations of primary and secondary elements to new and unique formations. In this highest class are included the phenomena of thought and of the constructive imagination. An extremely vivid impression of the extraordinarily complicated life which psychology undertakes to exploit is conveyed by the thirty odd pages or so devoted to the elucidation of these distinctions and to the exhibition of the rich interdependence of the elements and processes as they present themselves in the di- verse stages of mental development. The divisions thus drawn suggest the scheme for the distribution of the material in the second "special" part. Two chapters on sensation and sensations are followed by two on the affective anc volitional phenomena of the primary stage, and these by two or the secondary phenomena of reproduction and on the most im- portant products of the reproductive process, time, space and the distinction between the ego and its states and the external world of objects ; then comes a chapter on language and thought, followec by two concluding chapters treating respectively of the feelings and of the volitional phenomena of the secondary and tertiary stages. The chapters on sensation and sensations, filling more than 200 pages, bear witness to the relatively advanced state of our know- ledge in this department, of which they afford an admirably clear and an unusually complete conspectus, combined with a judicious handling of the most interesting and important matters of contrc versy. Original investigators may find ground for complaint in the omission of this topic or that which they may deem important and in the failure to notice some latest monograph ; the impartu critic will rather praise the author's learning, the rare good judg- ment shown in the selection of the matters most essential and the masterly manner of presentation. The general student will no- where find the mass of material which in this department has beer so rapidly accumulating in recent years better disposed to his ser- vice. It is unnecessary, nor is there here space, to go into details I will only refer especially to two points, and first, to the excellent discussion of psychophysical measurements. The technical ques- tions concerning the methods of investigation, of fundamental in- terest for the experimentalist, are, to be sure, not entered upon ; the author contents himself with a more summary exhibition of aims,