Henry Cavendish establishes the gravity constant to determine the density of the earth. His apparatus was much less complex. He used telescopes and light to measure the small increments of movement in his apparatus. The apparatus consisted of suspended weights that attracted each other. There were many problems to face other than measuring small amounts of movement. Turbulence played a large role in the movement that left error. He dealt with this by building a ten foot by ten foot room which concealed most turbulence. Also, he measured known turbulence that occurred and use that to correct the data. This led to the gravitational constant that we have today.
The picture is a modern apparatus for presenting the effects of gravity.
McCormmach, Russell. "Mr. Cavendish Weighs the World," American Philosophical Society, Vol. 142, No. 3. (Sep., 1998), pp. 355-366.