It is convenient to introduce the function =log =log (Q / q) + 01 (4) so that the polygon representing 12 conformally has a boundary given by straight lines parallel to the coordinate axes; and then to determine S2 and w as functions of a variable u (not to be confused with the velocity component of q), such that in the conformal representation the boundary of the and w polygon is made to coincide with the real axis of u.