xviii
THE ELEMENTS OF EUCLID.
BOOK I.
DEFINITIONS.
I.
A point is that which has no parts.
II.
A line is length without breadth.
III.
The extremities of a line are points.
IV.
A straight or right line is that which lies evenly between its extremities.
V.
A surface is that which has length and breadth only.
VI.
The extremities of a surface are lines.
VII.
A plane surface is that which lies evenly between its extremities.
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 rectilinear angle is the inclination of two straight lines to one another, which meet together, but are not in the same straight line.
