This, as Professor Thouless pointed out, has the further advantage of being the commonsense view. To the man in the street, who likes simple mechanical analogies, it appears self-evident. Its disadvantage is that it happens not to be true. Unquestionably it has led to immense progress in our understanding of the peripheral aspects of vision—what is hap. pening in the eye and in the optic nerve—but it will not give a complete account of how we actually see.
*One can easily start a dispute, Professor Thouless observed, "between a group of people when driving through the country by asking them whether the cows in a distant field look larger or smaller than a sparrow perched on the hedge. The answers will be very different, and each will think that he is giving the only- reasonable answer." This is because an object seen at a distance looks larger than an object whose image on the retina is of the same actual size, but which is/Close at hand; but the degree to which it looks larger than it ought to varies very considerably with different individuals.
He detailed a number of observations he had made, using a simple experiment which anyone can repeat. An ellipse of white paper is cut out, and the observer, beginning with his eyes immediately above it, moves his head away and down, keeping it so that he is always looking along the long axis of the ellipse. The ellipse will appear less elongated until at one point it looks circular; after this, as the head is moved still farther down, it will, of course, again appear as an ellipse, but this time with its long axis set transversely.
Text read from the printed page and cleaned; old type leaves the occasional error.