In this paper, the writer introduces the formulae to convert the geographical latitude on the ellipsoid to the authalic or equivalent latitude on the authalic sphere (formula 13 of the Chinese text) and the isometric latitude on the isometric sphere (formula 25). These formulae are obtained by series expansion, of which the term rnntaining the 6th power of the eccentricity of the ellipsoid has been omitted. The maximum error by neglecting this term amounts respectively to 0".Ol for the authalic latitude and 0".006 for the isometric. Two tables, one for conversion of geographical to authalic latitude and the other to isometric latitude are appended at the end of paper. They are calculated for the ellipsoid of Kras-sowski.