Atomic size

Einstein's equation enabled the calculation of atomic and molecular sizes from Brownian motion. Perrin confirmed this by observing suspended particles through a microscope, relying on Einstein's equations to make his determinations. Atoms, it turned out, are about a hundred-millionth of a centimeter in diameter.
 Jean-Baptiste Perrin France 1908 Atomic size

Einstein's equation enabled the calculation of atomic and molecular sizes from Brownian motion. Perrin confirmed this by observing suspended particles through a microscope, relying on Einstein's equations to make his determinations. Atoms, it turned out, are about a hundred-millionth of a centimeter in diameter.