CHAP. VII. Of LINES.
IT may be remember'd that in the introduction, the reader is desired to consider the surfaces of objects as so many shells of lines, closely connected together, which idea of them it will now be proper to call to mind, for the better comprehending not only this, but all the following chapters on composition.
The constant use made of lines by mathematicians, as well as painters, in describing things upon paper, hath establish'd a conception of them, as if actually existing on the real forms themselves. This likewise we suppose, and shall set out with saying in general—That the straight line, and the circular line, together with their different combinations, and variations, &c. bound, and circum|scribe all visible objects whatsoever, thereby producing such endless variety of forms, as lays us under the ne|cessity of dividing, and distinguishing them into general classes; leaving the intervening mixtures of appearances to the reader's own farther observation.
First, * 1.1 objects composed of straight lines only, as the cube, or of circular lines, as the sphere, or of both to|gether, as cylinders and cones, &c.