<s id="A18-1.13.01">[13] If a line moves around a point and one assumes on this line two points that, starting at the fixed point, divide the line according to a given ratio, then the two points that are moving with this line will determine similar figures.</s>
<s id="A18-1.13.02">If the line moves in a plane, the determined figures will be planar.</s>
<s id="A18-1.13.03">If the line, however, does not move in a plane but in a body, then the determined figures are solid, if we assume that the points in their close proximity to one another describe the surfaces of the figures.For nothing prevents this sentence to be assumed among the things that are perceptible by the senses; among those that are only imagined it is even more true and correct.</s>
<s id="A18-1.13.04">From another point of view figures are called similar when one draws the one inside the other and assumes one point so that the lines, drawn from that point towards the borders of the figures, be they lines or planes, are intersected by the borders of the figures in that ratio.</s>
