60. Having drawn a line of a certain shape, either straight or angular
or curved, or partly angular, partly curved, we may change the measure
of the line, in its length, without changing its shape. That is to
say, we may draw the line longer or shorter, keeping all changes of
direction, such as they are, in the same positions, relatively. In that
way the same shape may be drawn larger or smaller. That is what we mean
when we speak of a change of scale or of measure which is not a change
of shape.