not have been properly placed. Ifthe latter is the case, he should alter the circleand examin it with his eye until it is precisely placed that is, until he findsthat by mov g his eye round the hole’s circumference he will see thecircumference of the circle and nothing beyond It.[56] When this circle has been precisely placed, I let him turn to the inclinedhole and, placing his eye at its circumference, look at the white wall.
He willperceive the circle drawn on this wall and its circumference and nothing more.Further, if he moves his eye round the circumference of the inclined hole,while looking at the farthest perceptible point on the wall, he will perceive thecircle and its circumference and nothing more, or less.
57] For the ratio of the line between the centres of the two far circles on theinterior surface of the wooden blockto the line between the centres of the two opposite circles on theexterior surface,is as the ratio of the line extending along the axis of the perpendicularhole between the centre of the interior circle and the surface of the white wallto the part of this line between the two walls.