After taking a look at the accompanying illustration you will be positive that the cords shown run in a spiral toward the center, yet it shows a series of perfect circles of cords placed one inside the other. You can test this for yourself in a moment with a pair of compasses, or, still more simply, by laying a point of a pencil on any part of the cord and following it round. Instead of approaching or receding from the center in a continuous line, as in the case of a spiral, you will find the pencil returning to the point from which it started.

Ill: The Cord Is Not a Spiral