The first sentence of section (2) should read;For equatorial lines a 1 = 90° exactly, 'Y = y = 1 , and r = 1-'Y 2 = 0.However, I feel that the mathematical development given by the section would be well applicable to all cases, including the case a 1 = 0 exactly, but clearly the real need was for the special case of the line on the equator.