To test this part of the theory, Capasso and his colleagues measured the force between a gold-coated polystyrene sphere 40 microns in diameter and a plate made either of gold or of silica, all immersed in the organic liquid bromobenzene. They mounted the tiny sphere on the arm of an atomic force microscope, and used lasers to detect the bending of the arm as they brought the sphere closer to the plate. From that they could calculate the force on the sphere.