Where can I find a paper or reference that describes the timeline of measurements of the magnitude of the electron's electric charge.

For context, Millikan's oil drop experiment in 1908 determined the charge of the electron to be 1.59*10^(-19) C, which is lower than today's accepted value. Richard Feynman is quoted as saying, in 1974, that subsequent experimental attempts to measure the charge were biased by Millikan's initial value:

[...] It's interesting to look at the history of measurements of the charge of an electron, after Millikan. If you plot them as a function of time, you find that one is a little bit bigger than Millikan's, and the next one's a little bit bigger than that, and the next one's a little bit bigger than that, until finally they settle down to a number which is higher.

Why didn't they discover the new number was higher right away? It's a thing that scientists are ashamed of—this history—because it's apparent that people did things like this: When they got a number that was too high above Millikan's, they thought something must be wrong—and they would look for and find a reason why something might be wrong. When they got a number close to Millikan's value they didn't look so hard. And so they eliminated the numbers that were too far off, and did other things like that...

Is there a reference that shows the temporal evolution of the electron's charge values? The most I've found is a statement that the values did change, but not what those values were.

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    $\begingroup$ I've heard a similar thing said about the history of estimates of the speed of light, although it was more extreme: one early result "anchored" several subsequent results on values that were significantly off... $\endgroup$
    – Seamus
    Commented Nov 24, 2014 at 16:37

2 Answers 2


If anyone's still reading this thread, here's a few more data points that appear to back Feynmann's interpretation.

Erik Bäcklin, Nature vol 123, no. 3098, p. 409 (1929): $1.59875 \cdot 10^{-19} \pm 0.004796 \cdot 10^{-19} $.

Wide error bar overlaps Millikan's.

Gunnar Kellstrom, Phys. Rev. 1935: $1.60709 \cdot 10^{-19} \pm 0.011 \cdot 10^{-19} $.

Revises Millikan's value based on updated viscosity of air. Wide error bars!

H.R. Robinson, 1937 Rep. Prog. Phys. 4 212: $4.803 \cdot 10^{-10} \, \text{esu} = 1.602 \cdot 10^{-19} \, \text{C}$

Concludes with a note added at the proof stage: "Backlin and Flemberg’s result, however, comes down to $4.778\cdot10^{-10}$--or very nearly to Millikan's 1917 value! This is a most unfortunate note on which to end the Report."

Oil drop charge--historical reports

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    $\begingroup$ I favorited this question two years ago in hopes of more information. Your necromancy does not go unappreciated. :) $\endgroup$
    – David H
    Commented Nov 4, 2016 at 9:22
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    $\begingroup$ Excellent research, thanks. And also a wonderful example of why open science is necessary. Millikan was quite ruthless in purging suspected outliers, it seems... $\endgroup$ Commented Mar 9, 2021 at 8:30

The 16th (1995) edition of Kaye and Laby includes the following progression of the accepted values for the charge of an electron. The first value "is essentially Milikan's oil drop value" and the second is "the 'X-ray grating' value". I couldn't find any more details about the actual experiments. The standard errors are often over-optimistic, indicating unexpected systematic errors; in Milikan's case this was due to an inaccurate value for the viscosity of air.

  • 1.5911 ± 0.0024 [Birge, 1929]
  • 1.60203 ± 0.00050 [Birge, 1942]
  • 1.60210 ± 0.00002 [Dummond and Cohen, 1963]
  • 1.602192 ± 0.000007 [Taylor et al, 1969]
  • 1.6021892 ± 0.0000046 [Cohen and Taylor, 1973]
  • 1.6021773 ± 0.00000049 [Cohen and Taylor, 1987]

enter image description here

Interestingly, this doesn't really seem to bear out Feynmann's assertion. However, it would be useful to see the progression of values between 1929 and 1942: e.g. from K&L 8th edition (1936).

  • 2
    $\begingroup$ A snippet from books.google.co.uk/books?id=VP9UAAAAMAAJ (1938) states "This series of experiments gave the value of the electron charge as 1.59 X 10-19 coulomb, the value which has been used until 1936, when a slight correction was discovered. The value now accepted is 1.60 X 10-19 coulomb." $\endgroup$
    – Uri Granta
    Commented Mar 8, 2015 at 12:37

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