A development by Helmert (1901) of the formula for gravity acceleration, using the measurements of gravity available at the time but not using any pre assigned value of the Earth's flattening. Referred to the Potsdam value of gravity, Helmert's gravity formula of 1901 is τ _o = 978.030 (1 + 0.005302 sin²φ - 0.000007 sin²2φ). While the International Gravity Formula is based on a pre assigned value of the Earth's flattening, the above formula is not but was used in determining a value for the flattening, namely, 1/298.2. The coefficients 978.030 (τ _e) and 0.005302 (β ₁) were determined from the measurements. Attempts made to determine the coefficient of sin²2φ in the same way were abandoned because of the large probable errors that resulted, and the value 0.000007 was based on Darwin's and Weichert's theories of the figure assumed, at equilibrium, by a rotating, liquid body of the size of the Earth. Such a body, unless homogeneous, will not be exactly ellipsoidal in shape but will, in middle latitudes, lie below an ellipsoid (rotational) having the same lengths of major and minor axes. The amount of this depression will depend upon the law used to express the variation of density with respect to distance from the Earth's center. Darwin and Weichert assumed different laws but both found a depression of 3 meters at latitude 45^o. This depression corresponds to the difference between 0.0000059 and 0.000007, the corresponding coefficients in the International and the Helmert gravity formulae.