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410 Distance estimated by it. One of the means by which the distances of visible objects are judged of, is the muscular effort by which the obliquity corresponding to their binocular parallax is given to the optic axes. The greater that effort is, the nearer will be the object looked at. According to Professor Muller, the effort by which the eyes are adjusted to distinct vision at varying distances, is always simul- taneous with that by which the obliquity of the optic axes is made to accord with the binocular parallax. So invariable is this coin- cidence, that the axes cannot be directed to any near point, even by an effort of the will, without the other internal adjustment of the eye for distinct vision taking place. prev next |