The String and Balls Puzzle
Get a thin piece of wood, bone, or ivory, of the shape shown in the annexed figure (Fig. 10); bore in it three holes—one at each end, and one in the middle. Pass a piece of string or twine through the middle hole, leaving a loop, as shown; on each side of the string thread a ball or ring, and fasten the two ends of the string with knots at the holes at the end of the piece of wood. The puzzle is, without removing the string from the holes or without untying the knots, to get both balls or rings to the same side of the central loop instead of on opposite sides. The following is the solution of the puzzle:—Draw the central loop of the string well down, and slip through it either one or other of the balls until it reaches the back of the central hole; then pull the loop through the hole, and pass the ball through the two loops that will thus be formed; draw the string back through the hole as before, and the ball may easily be passed to that part of the string on which the other ball has been strung. This plan of passing the loop through the central hole is a key to all the puzzles of this nature. Such puzzles appear under various names, but they may all be solved if the key to this puzzle of the Balls and String is borne in mind.
A somewhat similar, although more complicated puzzle, is that known as