Milikan Oil Drop
References
[1] R. Millikan. On the elementary electrical charge and the avogadro constant. Phys. Rev., 2:109, 1913. Available at https://doi.org/10.1103/PhysRev.2.109.
[2] M. Fletcher. Rememberin the oil drop experiment. Physics Today, 60:56, 2007. Available at https://doi.org/10.1063/1.2743125.