“I lately witnessed a beautiful illustration of this subject at the Royal Institution,” said Mr. Seymour. “A number of cogged wheels, cut out of pasteboard, were set in motion in a perfectly dark room, when occasional flashes of light from an electric battery, displayed their forms most distinctly, and yet although whirling round at the time, they appeared to the spectator as motionless as so many solid blocks of marble. In like manner, in a storm during the darkness of midnight, the rolling ship and waves, when rendered visible by flashes of lightning, will appear as completely at rest, as a representation of them upon the canvass.[68a] I may at some future time extend this interesting subject, by exhibiting some optical illusions produced by the revolution of wheels in different directions, and at different velocities, for the knowledge[69] of which we are indebted to Mr. Faraday, and in mentioning that distinguished philosopher,” added Mr. Seymour, addressing himself more particularly to the vicar, “I cannot avoid remarking, that if _Philosophy in Sport_ can be made _Science in Earnest_, the juvenile lectures delivered by that professor have established the converse proposition, that the sternness of Science may be relaxed into the engaging aspect of Sport.” “Before quitting this subject,” continued he, “I have yet another toy in store for your amusement; it is founded upon the optical principle which I have every reason to believe you now thoroughly understand.” A square box was then produced containing a number of card discs, the edges of which exhibited a series of notches corresponding with the figures delineated on their margins. That the reader may better understand their construction, as well as the explanation of Mr. Seymour, the following representation has been introduced. [Illustration: As explained above. Figure is a dark-skinned man jumping in the air.] “To exhibit the magical effects of this toy,” said Mr. Seymour, “I will, by means of the spindle to which it is attached, cause it to revolve rapidly before the looking-glass, and you shall view the reflection through the openings.” Each member of the party obeyed in succession the direction thus given, and severally expressed the great astonishment they felt, at observing the figures in constant motion, and exhibiting the most grotesque attitudes.