Passage IV

NATURAL SCIENCE: This passage is adapted from Free Radicals by Michael Brooks (@2011 by Michael Brooks).

As the twentieth century began, Robert Millikan was fast approaching forty. All around him, physics was as its most exhilarating, yet Millikan had done practically nothing. So he decided to measure e, the charge on the electron.

Millikan’s idea was simple. A droplet of water that had been given an electric charge would be attracted to a metal plate which carried an opposite charge. He arranged his apparatus so that the electrical attraction pulled the droplet up, while gravity pulled it down. This gave him a way to measure e. First he would find the mass of the droplet. Then he would measure the voltage needed for the attraction to the metal plate to cancel out the downward pull of gravity. From those two pieces of information he could get a measure of the charge on the droplet.

The experiment was far from simple to carry out, however. Finding that the water droplets tended to evaporate before any measurements could be made, Millikan set to the task of trying the same trick with oil droplets.

In 1910, at the age of forty-two, he finally published a value for e. It was meant to be his career-defining publication. Eventually, it was—but Millikan still had years of difficult and dirty work ahead of him.

The Austrian physicist Felix Ehrenhaft refuted Millikan’s results with a similar set experiments that seemed to show that electrical charge can be infinitely small. There is no fundamental, minimum unit of charge, Ehrenhaft said; there is no ‘electron’. The series of experiments the desperate Millikan then performed were to cast a lasting shadow over his scientific integrity.

According to biologist Richard Lewontin, Millikan ‘went out of his way to hide the existence of inconvenient data’. David Goodstein, a physics professor, says Millikan ‘certainly did not commit scientific fraud’. So where does the truth lie?

The debate hangs on a phrase in Millikan’s 1913 paper refuting Ehernhaft and showing that every measurement of electric charge gives a value of e or an integer multiple of e. In his 1913 paper, Millikan says that his data table ‘contains a complete summary of the results obtained on all of the 58 different drops upon which complete series of observations were made’. The statement is written in italics, as if to give it special weight. The notebooks for the 1913 paper show that Millikan actually took data on 100 oil droplets. Did Millikan cherry-pick the data in order to confirm his original result and crush Ehrenhaft underfoot?

He certainly had motive. In Millikan’s 1910 paper he had made the ‘mistake’ of full disclosure with statements such as, ‘Although all of these observations gave values of e within 2 percent of the final mean, the uncertainties of the observations were such that ….I felt obliged to discard them’. This admirable honesty about the selection of data points had given Ehrenhaft ammunition that he used enthusiastically in his long feud with Millikan, Perhaps, with the italicized statement, Millikan was making sure that he gave his foe no more.

That would certainly explain something that is otherwise inexplicable. Millikan aborted the experimental run on twenty-five of the droplets in the work reported in the 1913 paper. According to Goodstein, Millikan preferred to use droplets that showed a change in charge, gaining or losing an electron (as he saw it) during the measurement. Millikan may also have judged some droplets to be too small or too large to yield reliable data, Goodstein says. If they were too large, they would fall too rapidly to be reliably observed. Too small, and their fall (and thus the charge result) would be affected by random collisions with air molecules. Goodstein interprets the italicized statement as an assertion that there were only fifty-eight ‘complete enough’ sets of data.

But Goodstein undoes his defence by stating that in order to make the ‘too large’ or ‘too small’ distinction, all the data would need to have been taken in first place.

Millikan certainly did not convince his peers straight away. The arguments with Ehrenhaft rumbled on long enough for Millikan’s Nobel Prize to be delayed for three years——it eventually came in 1923.

But here’s the point: Millikan was right about the electron and its charge. Few laboratories managed to replicate Ehrenhaft’s result, but students now replicate Millikan’s results, all across the world. No one now believes that fundamental unit of charge is anything other than Millikan’s e.

To get his Nobel Prize, Millikan had to play hard and fast with what we might call ‘accepted practice’.