In the London Philosophical Transactions of 1825, Dr. Roget .describes and explains a curious optical deception, which presents itself, when a person looks through a series of narrow vertical apertures at a carriage wheel, as it rolls along on the ground. The wheel appears to have simply a progressive, without a rotary motion, as though it were sliding, and the spokes seem to be more or less curved. The two spokes, however, which are in a vertical line, and therefore coincident in direction with the apertures through which the observer looks, remain in appearance, straight, while all the others, both on the right and left, have considerable curvature, presenting their concavity upward, or towards the highest spoke.