Search Loci: Convergence:
Whereas at the outset geometry is reported to have concerned herself with the measurement of muddy land, she now handles celestial as well as terrestrial problems: she has extended her domain to the furthest bounds of space.
Hodder and Stoughton, The Story of Euclid. 1901.
Van Schooten's Ruler Constructions
Solution to Problem VII
Problem VII: Given an indefinitely long line AB and a point C away from it, to draw CF which makes an angle with the given line AB which is equal to a given angle E.
Construction: To the point A in AB, construct, following the previous problem, and angle DAB, equal to E, and draw C, from the 3rd problem, line CF parallel to the line AD: I say the angle CFB is equal to the angle E.