Quiz: Remember the definition of mal de mer?
curve cutting the meridians of a sphere at a constant nonright angle. Thus, it may be seen as the path of a ship sailing always oblique to the meridian and directed always to the same point of the compass. Pedro Nunes, who first conceived the curve (1550), mistakenly believed it to be the shortest path joining two points on a sphere (see great circle route). Any ship following such a course would, because of convergence of meridians on the poles, travel around the Earth on a spiral that approaches one of the poles as a limit. On a Mercator projection such a line (rhumb line) would be straight. Rhumb lines are used to simplify small-scale charting