An Essay Towards a New Theory of Vision

If I do not perceive the redness or paleness of a man's face themselves, it is impossible I should perceive by them the passions which are in his mind. 11. Now from sect. 2 it is plain that distance is in its own nature imperceptible, and yet it is perceived by sight. It remains, therefore, that it be brought into view by means of some other IDEA that is itself immediately perceived in the act of VISION. 12. But those LINES and ANGLES, by means whereof some MATHEMATICIANS pretend to explain the perception of distance, are themselves not at all perceived, nor are they in truth ever thought of by those unskilful in optics. I appeal to anyone's experience whether upon sight of an OBJECT he computes its distance by the bigness of the ANGLE made by the meeting of the two OPTIC AXES? Or whether he ever thinks of the greater or lesser divergency of the rays, which arrive from any point to his PUPIL?