jan 1, 1910 - Robert Millikan Discovery

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He succeeded in precisely determining the magnitude of the electron's charge.
The Oil Drop Experiment: He sprayed tiny drops of oil into a chamber. First calculated a constant. Then, he sprayed oil drops and applied an electrical charge to them by shining x-rays into the chamber. The x-rays ionized the air, causing electrons to attach to the oil drops. The oil drops picked up static charge and were suspended between two charged plates. He was able to observe the motion of the oil drops with a microscope and discovered that the drops lined up in a specific way between the plates, based on the number of electrons they had.

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