Thus the contrary flow has become circular, (actually it's usually oval.) - This remark points to the cause of the present controversy: a circle is generally considered a geometrical figure, all points of which are at the same distance from the centre. The adjective circular however, is often used in a topological rather than geometrical sense: a circular path simply has no beginning nor end, and its shape is irrelevant and can be very involved. An eddy is a is a circular path of water molecules - or electrons. Which is the direction of the mainstream - does not matter for the eddy.