ABSTRACT
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 illusion is the same, if the wheel revolve on a fixed axis, while the vertical bars have a progressive motion between it and the observer. The direction in which the spokes appear to be bent may, however, be reversed in this form of the experiment. If the bars move in the same direction as the lower part of the revolving wheel, the concavity of the spokes will be upward; if in the same direction as the top of the wheel, the concavity will be downward.
