OPTICAL ILLUSION—CAT'S EYE TIMEPIECE

[Extracted from Knowledge, vol. 1, Feb. 1882, p. 344.]



[279]—In the long string of optical illusions which have appeared from week to week in your esteemed paper, I am surprised the following has not been mentioned:—Fix an ordinary fork in the wall, and on the handle balance a small cork. Having shut the right eye, walk towards the cork and endeavour to knock it off with the little finger. It is very seldom that the cork is displaced upon first trial.

Your account of the remarkable ingenuity of the Chinese in calculation reminds me of the peculiar manner in which they are able to approximately tell the time, no matter whether the day is cloudy or dull. They will run to the nearest cat, open her eyes, if they are not already open, and will at once inform you, with a certain amount of accuracy, what time it may be; all depending, of course, upon the contraction of the iris or the size of the aperture of the pupil of the eye. What I cannot understand in connection with this process is, why the clouds in interrupting the sun's light have no effect upon the cat's eye? But I suppose the Celestial land knows not what fogs and mists are, and therefore we should not be able to avail ourselves of the advantage of feline clocks here. Even if it were so, I question whether pussy would submit with such grace as the rats in the land of the pigtail seem to, to an operation which must of necessity be far from agreeable to her.

Yours, &c.,

ERNEST J. WERNHAM