It is an improved, small sized apparatus based on Henty Cavendish experiment structure, which can be used for observing interactive force among maters, also can be sued for measuring Universal Gravitational Constant G=6.67x10-11 NM2/Kg2 and showing relations of F∝1/r2. This classic instrument is used to measure the value of G (gravitational constant) the same way Sir Henry Cavendish did in 1798. Consists of a pair of small lead balls mounted on a 揟?member suspended w/ a thin wire and a pair of large lead balls. Oil damping is provided for faster results. Requires a laser (not included). Instruction manual included.