The Most Famous Successful Experiment

In a recent article titled The Most Famous Failed Experiment, we saw how Albert Michelson and Edward Morley in 1887 failed to prove the existence of ether and left scientists without a transmitting medium for light. But failure and success sometimes can co-exist. The Michelson-Morley experiment opened the path to Einstein’s relativity theory which became a cornerstone of modern physics.

We shall take a more positive outlook today and describe one of the most successful experiments of the twentieth century. The oil drop experiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the charge of the electron was a stunning success in its scientific outcome and yet very controversial in its circumstances.

I won’t dwell on the scientific details, which most of you have learned in high school, but we can just briefly review the experimental concept. The apparatus was a closed chamber with two horizontal metal plates connected to an external battery. Oil drops were sprayed into the space between the metal plates. With the use of X-rays, the oil drops were given an electric charge. With the battery turned off there was no electric field, and the oil drops would fall freely…