THE ELEMENTS OF EUCLID. BOOK I. DEFINITIONS. I. A POINT is that which hath no parts, or which hath no magnitude. A line is length without breadth. II. III. The extremities of a line are points. IV. A straight line is that which lies evenly between its extreme points. V. A superficies is that which hath only length and breadth. VI. The extremities of a superficies are lines. VII. A plane superficies is that in which any two points being taken,* the straight line between them lies wholly in that superficies. VIII. "A plane angle is the inclination of two lines to one another* in a plane, which meet together, but are not in the same direction." IX. A plane rectilineal angle is the inclination of two straight lines to one another, which meet together, but are not in the same straight line. |