The Greek philosophers debated whether matter is infinitely divisible, or composed of discrete atoms (the word atom means "indivisible"). In the 19th century the atomic idea was the basis for several successful theories of chemistry and physics, such as Dalton's theory of chemical combination and Maxwell's kinetic theory of gases. Further Einstein's theory about quantization of energy and Rutherford's model of the atom inspired Millikan to examine the possible quantization of electric charge through this experiment.