of as intersecting each other at a point, which has no dimensions and is only of the thickness (if thickness it may be called) of one single line.
HOW WE MAY CONCLUDE THAT A SUPERFICIES TERMINATES IN A POINT?
An angular surface is reduced to a point where it terminates in an angle. Or, if the sides of that angle are produced in a straight line, then—beyond that angle—another surface is generated, smaller, or equal to, or larger than the first.
48.
OF DRAWING OUTLINE.
Consider with the greatest care the form of the outlines of every object, and the character of their undulations. And these undulations must be separately studied, as to whether the curves are composed of arched convexities or angular concavities.
49.
The nature of the outline.
The boundaries of bodies are the least of all things. The proposition is proved to be true, because the boundary of a thing is a surface,