Measurement of Density Inhomogeneity for Glass Pendulum

The density inhomogeneity of a glass pendulum is determined by an optical interference method. The relative variations of the densities over a volume with sizes of 5×5×5mm³ are (0.64\pm 0.97)×10^-5 and (0.99±0.92)×10^-5 for the K9 glass and silica glass pendulum, respectively. These variations of densities contributing to the relative uncertainties of the Newtonian gravitational constant G are 0.20ppm and 0.21ppm in our experiment on measurement of G.