Precise Determination of Separation Between Spherical Attracting Masses in Measuring the Gravitational Constant

A rotating gauge method is used to measure the span between two spheres with high precision in determination of the gravitational constant G. A rectangular gauge block slightly shorter than the span is located horizontally between two spheres, and the angle between two symmetric bounding points during rotation can be determined by measuring the shift of a laser beam passing through an optical plate fixed on the gauge block. Experimental results show that the uncertainty in the determination of the span between the two spheres is less than 0.5 μm.