424 PHILOSOPHICAL PEEIODICALS. I. Ordinary binocular vision. (1) The illusion with a monochromatic figure of uniform brightness is greater, the greater the brightness differ- ence between background colour and figure colour. The decrease of the illusion with decrease of the brightness difference extends, however, only to a certain point, beyond which it increases. With a bichromatic figure of different brightness, the illusion is greater the greater the given bright- ness difference between transverse line and ground, and the less the brightness difference between principal line and ground. If the former is constantly decreased, the latter increased, the magnitude of the illusion approximates constantly to zero. (2) Over and above the misplacement value (Ablenkungsvalenz) due to the brightness difference of figure and ground (transverse line and ground, principal line and ground), there is also a chromatic misplacement value in the narrower sense, primarily for green and violet. (3) The illusion decreases as the field of observa- tion decreases. The influence of eye movement along the principal line is, with monochromatic figures of equal brightness, indirectly to decrease the illusion ; with bichromatic figures of different brightness, to increase or decrease it, according to special conditions. (4) As regards the maximal values of the illusion with the two classes of figures, the observers fell into three well-marked groups. II. Haploscopic observa- tion. (1) With monochromatic figures of equal brightness, haploscopic combination of the parts reduces the illusion. The illusion is still a function of the brightness difference of figure and ground. A chromatic misplacement value is again recognisable. (2) With bichromatic figures of different brightness, the colour difference of transverse and principal lines reduces the illusion, even where other factors would lead us to expect its increase. A distinction must be made between the misplace- ment value of colour and the misplacement value of insistency (Aufdring- lichkeit), the former being realised only in monochromatic, the latter only in bichromatic figures. Colours that have no misplacement value, as colours, possess a misplacement value of insistency and conversely. A theoretical discussion of these facts is promised.] O. Rosenbach.
- Zur Lehre von den Urtheilstauschungen.' [If figures (triangles, ovals,
oblongs, angle-pieces, etc.) have their centres covered by a horizontal strip of paper (black, white, coloured), the covering appears, under certain conditions of observation, to be transparent ; so that the central parts are seen as if through a veil. Since irradiation and after-images are ruled out, the author ascribes this phenomenon to a pure illusion of judg- ment. As, however, the supplied central parts are always outlined in accordance with the law of least resistance of eye movement (rounded, etc.), the influence of the sense organ must be admitted. The writer accordingly distinguishes three causes of illusions of judgment : inductive and deductive autosuggestion, and the effect of the physiological auto- matism of the organ of sense.] Literaturbericht. Bd. xxx., Heft 1 und 2. E. Riemann. ' Die Scheinbare Vergrosserung der Sonne und des Mondes am Horizont. I. Geschichte des Problems.' [Historical sketch of ex- planations, from Aristotle to von Zeheuder, Zoth and Schaeberle.] P. Ranschburg. ' Ueber Hemmung gleichzeitiger Eeizwirkungen. Experi- menteller Beitrag zur Lehre von den Bedingungen der Aufmerksamkeit.' [Experiments with the author's mnemometer (stimuli : series of printed numerals) gave the following results : (1) Two to four place numbers are simultaneously apprehended and correctly repeated, with an exposure of one-third of a second, both by educated and (in the great majority of cases) by uneducated observers. (2) Five and six place numbers require a much more intensive concentration of attention ; errors and subjective uncer- tainty appear, even with practised and educated observers. (3) The
