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1. Perceptual adaptation to a 30 or 45° visual tilt was induced in human subjects by means of prismatic spectacles worn for 5–7 days. Relative contrast thresholds and the amplitudes of the occipital potentials to vertical and oblique gratings were studied. 2. During continuous exposure to the tilted visual environment the normal differences between contrast thresholds for vertical and oblique targets decreased or were no longer significant. In all subjects the change from control threshold differences was significant at the 0·005 level. 3. During the course of adaptation the difference in amplitude of the potentials evoked by vertical and oblique oscillating gratings also decreased. The changes with respect to control differences were significant at the 0·005 level in each subject. 4. Intermittent exposure to tilt in one subject resulted only in minor adaptation of the apparent vertical, and the evoked potential differences did not change from control levels. 5. The changes are interpreted as suggesting that plastic changes in the extraretinal mechanism responsive to target orientation occur during adaptation to prismatic tilt.

Using a gas transpiration method, the equilibrium constant for the reaction ZnO(s) + H2(v)⇄ Zn(v) + H2O(v) was determined directly in the temperature interval 592–950°C. The data are described by the equation log10K = [-11.794 × 103/T] + 8.040 with ΔH° = 53.97 Kcal/mole and ΔS° = 36.79 e.u. Based on this Information, vapor-solid gas concentration curves useful for defining conditions for the chemical vapor transport of ZnO via the reverse of the above reaction have been computer calculated.