Marks' first lessons in geometry / In two parts. Objectively presented, and designed for the use of primary classes in grammar schools, academies, etc.

by Bernhard Marks

Diagram 24.

LESSON THIRTY-SECOND.

THE CIRCLE AND ITS LINES.

If the straight line c a were a string made fast at c, with a sharp pencil-point at the other end a, and the pencil-point were moved towards d, what line would be drawn?

What kind of a line would it be?

If the pencil-point continued to move in the same direction until it returned to the starting-point a, what curved line would be drawn, naming it by all the points in it which are marked?

The plane figure bounded by this curve is called a “circle.”

What point is at the centre of this figure?

A circle is a plane figure bounded by a curved line, all points of which are equally distant from the centre.