Binocular Vision

Abstract

THE ability to see stereoscopic pictures without a stereoscope, referred to by Mr. G. R. R. Bray in NATURE of Nov. 26, p. 959, is, if not common, at least fairly easy to acquire. I have been able to view such pictures, with, naked eyesight, for many years past. If one places a pair of stereoscopic pictures at the normal distance from the eyes for comfortable vision, and then directs one's gaze just over the top of the pictures at some more distant object, two images of each of the pictures will immediately appear. By a little practice, the right hand image of the left picture and the left hand image of the right picture can be brought into coincidence, the coincidence occurring rather suddenly in the end, and, as it were, engaging in that position. This sudden coalescence is, I presume, due to the eyes refocusing at normal distance each on its own picture. When this has occurred the equilibrium is fairly stable.