Geometrical Exercises with the Straight Edge

The straight edge or ruler, as a mathematical instrument, enables as to draw straight lines of indefinite length through one or more points. It is not helpful to set off definite lengths. Geometrical constructions in which the straight edge only is to be used naturally find a place in Projective Geometry, (Geometrie der Lage, Geometric de Position) in which metrical considerations are not, as in Euclidean Geometry, of primary importance. See : J. W. Russell's Elementary Treatise on Pure Geometry.