No. X.—THE SHIFTING BRICK
A very curious and interesting form of optical illusion is well illustrated by what may be called “the shifting brick.”
The central brick, drawn to show all its edges, as though it were made of glass, will assume the form indicated by one or other of the smaller bricks at its right and left, according to the way in which the eyes accommodate themselves for the moment to one pattern or to the other. If you do not see this at first, look steadily for awhile at the pattern you desire.
ASK A CYCLIST
13. Why does a rubber tyre leave a double rut in dust, and a single one in mud?
TODHUNTER’S UNIQUE PUZZLE PROBLEM
14. If two cats, on opposite sides of a sharply sloping roof, are on the point of slipping off, which will hold on the longest?