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Quantum yields for the photochemical decomposition of aqueous MnO4— have been measured under a variety of conditions using a sensitive method for measuring O2 production, first developed by Pringsheim and co-workers. The quantum yield was found to depend strongly on the wavelength of the light, slightly on temperature at the longer wavelengths, and not at all on the composition of the solution or on light intensity. Additional experiments were carried out which showed that the isotopic composition of photochemically produced O2 was independent of the O-isotopic composition of the solvent water. These results lead to the conclusion that the radiant energy absorbed by the MnO4— ion is converted with high probability into vibrational energy of the ground state, after which the ion dissociates thermally into MnO2 and O2 (in a single act) or cools down without dissociation (the position of the extra electron is uncertain). A possible quantitative theory which predicts fairly successfully the dependence of the quantum yield on wavelength is outlined.

Pictorial depth cues such as perspective projection, aspect ratio, and texture gradients can specify mathematically the slant of a planar surface. We performed experiments to measure the accuracy of human perception of surface slant from these cues. We calculated the perceived slant from judgments of the relative lengths of a pair of orthogonal lines embedded in the surface. Our results indicate that slant judgments are accurate to within 3 deg. This level of accuracy was achieved whether the cues were luminance differences or equiluminous color differences. We found no evidence of the recession to the frontal plane that has been reported by Gibson [J.J. Gibson, The Perception of the Visual World (Houghton Mifflin, Boston, Mass., 1950]) and others. We did find evidence suggesting that subjects do not make accurate depth estimates of disconnected surfaces. This may be the source of the discrepancy between our measures and those of Gibson and others. This research, combined with previous findings, supports a model of perception that involves at least two and possibly more representations of space: one local veridical representation of surface orientation derived primarily from pictorial cues and another global representation of observer-centered distance derived primarily from binocular disparity and motion parallax.