582 PHILOSOPHICAL PERIODICALS. deaf-mute tone scale tell for Helmholtz, though confirmation by autopsy is desirable.] T. Heller. ' Ueber Aphasie bei Idioten und Imbecillen. ' [Idiots and imbeciles cannot be classified by defects of speech : attention must be the basis of classification. There are two sorts of defects of speech : those which come from, and correspond to, the general defect of intelligence ; and those which are really aphatic.] Guillery. ' AVeitere Untersuchungen ueber den Lichtsinn.' [(1) Grey on white can be seen by a single retinal element when the photometric relations are 1 : T15 ; grey on black when they are 3'17 : 1. (2) The retinal distribu- tion of the brightness elements for daylight is different from that of the brightness elements for adaptation to dark. The former are perhaps the rods, the latter the cones.] Litteraturbericht. Bd. xiii., Heft 4 und 5. J. von Kries. ' Ueber Farbensysteme.' [A very clear and comprehensive paper. The writer finds a tri- chromatic system, shown in the equations (determined with the eye adapted for light, not for darkness) of the great majority of those endowed with normal colour vision ; and two typically different di- chromatic systems, deducible from it by reduction (subtraction of one colour component), and represented by the light -equations of the two forms of partial colour-blindness. Beside these, and standing in no determinable relation to them, is the monochromatic system of congenital total colour-blindness, which is identical with the colour system of trichromates and dichromates in twilight-vision. The^e results are brought into connexion with the author's general theory of vision.] L. W. Stern. ' Psychische Praesenzzeit.' [The different pro- cesses contained in a given time-period may constitute a unitary ' act of consciousness,' despite their temporal dissociation. Present time, in direct time perception, is a brief time-period. Times can be ' projected ' in reduced scale into the present time (cf. dreams). In ' primary ' memory we experience immediately, perceive, the identity of impression and image ; in true memory we infer it. The conscious present has a special most favourable or ' optimal ' duration for every special contents.] Litteraturbericht. Bd. xiii., Heft 6. H. Ebbinghaus. ' Ueber eine neue Methode zur Pruefung geistiger Faehigkeiten und ihre Anwendung bei Schulkindern.' [Methods previously employed are those of ' calculation ' (simple additions and multiplications) and ' memory ' (writing out of words heard). The new method is the method of ' combination '. A printed text is muti- lated, the length of the omitted syllables and words being roughly indicated by lines ; and the child is required to fill out the gaps as quickly as possible, keeping the sense of the passage in view.] T. Elsenhans. ' Nachtrag zu Ebbinghaus' Kombinationsmethode.' [Pro- poses to combine the memory method with that of Ebbinghaus, by having the unmutilated text read aloud before the filling out of the muti- lated pages is begun.] Breuer. ' Ueber den Einflussdes Maculapigments auf Farbengleichungen.' [Comparison of macular and extrainacular (central and paracentral) colour equations, undertaken at von Kries' suggestion. Absorption-values increase with decreasing wave-length. The living fovea is pigmented. As the absorption-values are not very considerable, it is improbable that individual differences are of any great moment.] G. Heymans. ' Erwiderung.' [Reply to Titchener.] Litteraturbericht. PHILOSOPHISCHE STUDIEN. Bd. xiii., Heft 2. G. A. Tawney. ' Ueber die Wahrnehmung zweier Punkte mittelst des Tastsinnes, mit Blicksicht auf die Frage der Uebung und die Entstehung der Vexirfehler.' [Weber's law that the limina are greater on the long than on the short
