Here is another example of what is known as the persistence of vision:—
Look fixedly for some little time at this grotesque figure, then turn your eyes to the wall or ceiling, and you will in a few seconds see it appear in dark form upon a light ground.
A PUZZLE NUMBER
The sum of nine figures a number will make,
Of which just a third will remain
If fifty away from the whole you should take,
Thus turning a loss to a gain.
It needs something more than mere arithmetic to discover that the solution to this puzzle is XLV, the sum of the nine digits, for if the L is removed, XV, the third of XLV, remains.
No. XXIII.—ANOTHER PARALLEL FREAK
Here is another curious illusion:—
The four straight lines are perfectly parallel, but the contradictory herring-bones disturb the eye.