In Defense of Robert Andrews Millikan

David Goodstein. American Scientist. Volume 89, Issue 1. Jan/Feb 2001.

Robert Andrews Millikan was awarded the Nobel Prize for physics in 1923, in large part for his pioneering measurement of the charge of the electron. He was a founder, first leader and all-around patron saint of the California Institute of Technology. In the first half of the 20th century, he was one of the most famous scientists in America. Yet he has been accused of male chauvinism, anti-Semitism, mistreating his graduate students and, worst of all, scientific fraud. Because Millikan, who died in 1953, remains something of a hero at my institution (Caltech), I felt a duty to investigate these allegations and, after doing so, became convinced that they are unreasonably harsh. To appreciate how I reached this conclusion requires, first, a broad understanding of the man’s life and career.

Millikan was born in 1868, the son of a Mid-western minister. He attended Oberlin College, earned a Ph.D. in physics from Columbia University, did some postdoctoral work in Germany and, in the last years of the 19th century, took a position at the brand-new University of Chicago, in a physics department headed by his idol, A. A. Michelson.

During the next decade, Millikan wrote some very successful textbooks, but he made little progress as a research scientist. This was a period of dramatic change in physics: Max Planck had kicked off the quantum revolution; Albert Einstein produced his theories of relativity and the photo-electric effect; and Jean Perrin’s experiments and Einstein’s theory on Brownian motion established forever that matter was made of atoms. Millikan made no contribution to these advances. Nearing 40 years of age, he became very anxious indeed to make his mark.

Earlier, in 1896, J. J. Thomson had succeeded in showing that the constituent particles in all cathode rays are electrically charged and have the same ratio of electric charge to mass. This was the discovery of the electron. The challenge Millikan took up was to measure separately the charge of the electron. Thomson and his colleagues in England had tried to do so by observing how an applied electric field changed the rate of gravitational fall of a charged cloud of water droplets. But the British investigators had not managed to obtain much precision with this method.

Mishandling Students?

Working with a graduate student named Louis Begeman, Millikan had the idea of applying a much stronger electric field than had previously been used in the hope of stopping completely the descent of the cloud. To Millikan’s surprise, what happened instead was that nearly all of the condensate dispersed, leaving only those few droplets that had just the right amount of charge to balance gravity. Millikan quickly realized that measuring the charge on individual ionized droplets was far superior to finding the average charge on a cloud.

Unfortunately, the single-droplet method had a serious flaw: The water evaporated too rapidly for accurate measurements. Millikan, Begeman and a new graduate student named Harvey Fletcher discussed the situation and decided to try a substance that evaporated more slowly. Millikan assigned Fletcher the job of devising a way to use mercury or glycerin or oil.

Fletcher immediately got a crude apparatus working, using tiny droplets of watch oil made with a perfume atomizer he bought in a drug-store. He could view the tiny droplets inside the experimental chamber by illuminating them with a bright light and focusing a specially designed “telescope” on them. Through the eyepiece he saw the oil droplets dancing around Brownian motion, caused by impacts of unseen air molecules. This phenomenon itself was of considerable scientific interest at the time.

Within a couple of years, Fletcher and Millikan had produced two results. One was an accurate value of the fundamental unit of electric charge, e. The other was a determination of the product Ne (where N is Avogadro’s number), which came out of observations of Brownian motion. Thus two separate scholarly reports were in order. The academic rules of that era allowed Fletcher to use a published paper as his Ph.D. thesis, but only if he was its only author. So the professor approached his student with a deal: Millikan proposed that Fletcher be sole author on the Brownian-motion work and that he, Millikan, be sole author on the electric-charge work.

No doubt Millikan understood that the measurement of e would establish his reputation, and he wanted full credit. Fletcher understood this too, and he was somewhat disappointed, but Millikan had been his protector and champion throughout his graduate career, so he had little choice but to accept. This coercion is the source of the assertion that Millikan mistreated his graduate students. And in this case, he probably did. Still, the two men remained good friends throughout their lives, and Fletcher saw to it that his account of this unflattering episode was not published until after Millikan’s death (and after his own).

Mishandling Data?

More troubling is the contention that Millikan cheated in his famous oil-drop experiment. This view is widespread. Indeed, in 1984 Sigma Xi published a booklet called Honor in Science, which includes a discussion about cooking data, meaning “retaining only those results that fit the theory and discarding others.” According to Honor in Science, it is a well-established fact that Millikan cooked his data. Did he really? To answer that question requires investigation of two others. What actually happened back in the period between 1910 and 1917? And how, much more recently, did Millikan come to be blamed for committing scientific fraud?

The accusation, very briefly, goes as follows. After his 1910 paper presenting his initial measurement of the fundamental unit of electric charge, Millikan found himself embroiled in controversy with a Viennese physicist named Felix Ehrenhaft, who using a similar apparatus found cases of electric charges much smaller than Millikan’s value of e. To refute Ehrenhaft’s assertion, Millikan (at this point working alone; Fletcher had received his doctorate and left) made a new series of measurements, published in 1913, in which the charge on every single droplet studied was, within a very narrow range of error, an integer multiple of a single value of e. The 1913 paper succeeded in dispatching Ehrenhaft and contributed significantly to Millikan’s 1923 Nobel Prize.

Awkwardly, an examination of Millikan’s private laboratory notebooks indicates that he did not in fact include every droplet for which he recorded data. He published the results of measurements on just 58 drops, whereas the notebooks reveal that he studied some 175 drops in the period between November 11th, 1911 and April 16th, 1912. In a classic case of cooking, the accusation goes, he reported results that supported his own hypothesis of the smallest unit of charge and discarded those contrary results that would have supported Ehrenhaft’s position. And, to make matters very much worse, he lied about it. Millikan’s 1913 paper contains this explicit assertion: “It is to be remarked, too, that this is not a selected group of drops, but represents all the drops experimented upon during 60 consecutive days, during which time the apparatus was taken down several times and set up anew.” (Emphasis in the original). Thus, Millikan is accused of cheating and then compounding his cheating by lying about it in one of the most important scientific papers of the 20th century.

For the Defense

Entries in Millikan’s private laboratory notebooks are indeed quite telling. A typical one shows a column of figures arranged under the heading G, for gravity. These were the times taken for a tiny droplet, a pin-point of light, to fall between scratch marks in the focal plane of his telescope. These measurements gave the terminal velocity of the drop when the force of gravity was balanced by the viscous drag of air. From this observation he could determine the size of the tiny sphere.

Such notebook entries also contain another column of numbers under the heading F for “field.” These were the times taken for the same drop to rise between the scratch marks under the combined influence of gravity, viscous drag and the applied electric field, which had been turned off during the G measurements. Having both F and G values made it possible to determine the charge on the drop.

Scrutinizing Millikan’s notebooks, one sees that the F measurements on a given drop shift markedly from time to time. These changes happened because the charge on the drop increased or decreased when it captured an ion from the air. Millikan made use of these obvious events to help deduce the number of units of charge on the drop through a series of laborious hand calculations. More than one of the entries in his notebooks show the result of a computation and then the comment “very low something wrong,” perhaps with an indication of what Millikan thought might have disturbed the measurement. Needless to say, such entries were not included in the 58 drops Millikan published.

At first glance, this procedure certainly appears questionable. But one needs to dig deeper. The notebooks also contain a calculation with the comment “This is almost exactly right, the best one I ever had!!!” And yet Millikan did not include this drop either in his crucial 1913 paper. These discarded measurements, the good and the bad, were all part of a warm-up period during which Millikan gradually refined his apparatus and technique, in order to make the best determination possible of the unit of electric charge. The first observation that passed muster and made it into print was taken on February 13th, 1912, and all of the published data were taken between then and April 16th. This period of roughly two months is what Millikan refers to when he talks about “60 consecutive days,” although the interval was actually a bit longer (63 days), in part because 1912 was a leap year.

During these nine weeks Millikan recorded in his notebooks measurements on roughly 100 separate drops. Of these, about 25 series are obviously aborted during the run, and so cannot be counted as complete data sets. Of the remaining 75 or so, he chose 58 for publication. Millikan’s standards for acceptability were exacting. If a drop was too small, it was excessively affected by Brownian motion, or at least by inaccuracy in Stokes’s law for the viscous force of air. If it was too large, it would fall too rapidly for accurate measurement. He also preferred to have a drop capture an ion a number of times in the course of observation, so that he could investigate changes as well as total charge, which had to be an integer multiple of the fundamental unit, e.

None of these attributes could be determined without recording some data on a candidate droplet. Thus, it should not be surprising that Millikan gave up on some drops mid-course, or that he later found that some of those he observed fully did not act consistently enough to incorporate into his analysis. He had no special bias in choosing which drops to discard: Allan Franklin of the University of Colorado reanalyzed Millikan’s raw data in 1981 and discovered that his final value for e and for its margin of error would barely have changed had he made use of all the data he had, rather than just the 58 drops he selected.

What scientist familiar with the vagaries of cutting-edge experimental work would fault Millikan for picking out what he considered to be his most dependable measurements in order to arrive at the most accurate possible result? In the 1913 paper, Millikan cites his value of e with an uncertainty of 0.2 percent-some 15 times better than the best previous determination. The current value agrees with Millikan’s number within his cited error bounds. The experiment was nothing less than a masterpiece, and the 1913 paper describing it is a classic of scientific exposition. Nevertheless, it contains the phrase “this is not a select group of drops but represents all of the drops experimented upon during 60 consecutive days,” which is manifestly untrue. The question is, why did Millikan mar his masterpiece with a statement that is clearly false?

Many years after the fact, the science historian Gerald Holton of Harvard University studied Millikan’s work and told the story of the Millikan-Ehrenhaft dispute, contrasting the published results with what he found in Millikan’s laboratory notebooks. Holton did not accuse Millikan of misconduct of any kind, but instead found in the unpublished laboratory notebooks an opportunity to compare a scientist’s public appearance and behavior with what went on in the privacy of the laboratory In 1982, two journalists, William Broad and Nicholas Wade, seized on Holton’s work and included a discussion of Millikan in a book about misconduct in science called Betrayers of the Truth. Here Broad and Wade, both of whom were then reporters for Science magazine, and both of whom now write for the New York Times, accused, tried and convicted Millikan of scientific misconduct.

Devilish Details

I believe that Broad and Wade misunderstood and exaggerated the importance of Millikan’s dispute with Erenhaft and that they did not appreciate the legitimacy of data selection in an experiment whose real purpose was not to refute Ehrenhaft, but rather to measure e with the greatest possible accuracy Still, Millikan’s paper contains that nagging and blatantly false, “all the drops experimented upon during 60 consecutive days…” To understand the significance of those words, one must recall that Millikan’s oil drops rose and fell under the influence of three countervailing influences: gravity, electricity and viscous drag. The first two of these forces were very well understood. For the third, the 19th-century hydrodynamicist George Stokes had produced an exact formula for a sphere moving slowly through a continuous fluid.

The conditions that would make Stokes’s law exact were well-satisfied in all respects except one: Millikan’s drops were so small that the air through which they moved could not safely be considered a continuous medium. The average distance between air molecules was not completely negligible compared to the size of an oil drop. For this reason, Stokes’s law could not be relied on absolutely

To deal with this problem, Millikan assumed, entirely without theoretical basis, as he stressed in his paper, that Stokes’s law could be adequately modified using an unknown term that was strictly proportional to the ratio of the distance between air molecules to the size of the drop, so long as that ratio was reasonably small. To test this idea, he purposely made some measurements with that damaging ratio larger than it had to be by pumping some of the air out of his experimental chamber.

Millikan also used a trick that any modern experimentalist would appreciate. He plotted a graph of all his data in such a way that, if his supposition proved correct, all the points would fall on a single straight line, and the position of the line on the graph would give the magnitude of the unknown term. Thus, if successful, this tactic would all at once demonstrate that his method was justified and give the necessary correction.

In Millikan’s published paper, he explains how the experiment is done and, with specific drops as examples, describes how he analyzed his data, using changes in the charge on a drop to help determine the total number of units of charge present. Then, he writes: “Table XX. contains a complete summary of the results obtained on all of the 58 different drops upon which complete series of observations like the above were made during a period of 60 consecutive days.” Millikan didn’t detail why he had not considered his evaluation of some drops to be sufficiently complete, and he miscounted a period of 63 days as 60 days, but those slips seem rather minor. The clear implication of this statement in his paper is that there were drops for which the data were not complete enough to be included in the analysis.

This sentence is followed by two pages of Table XX and an additional two pages showing the graph he used to evaluate his correction to Stokes’s law. Millikan then discusses his straight-line test of his correction and points out that “there is but one drop in the 58 whose departure from the line amounts to as much as 0.5 percent.” The very next sentence is the problematic, “It is to be remarked, too, that this is not a selected group of drops but represents all of the drops experimented on during 60 consecutive days….”

So the damning remark is made, not about whether charge comes in units or what the value of e is, but in regard to getting the correction to Stokes’s law right. Millikan is merely saying here that all of the 58 drops he just discussed confirm his presumed formula for amending Stokes’s law. And although this statement appears five pages after the remark that qualified the choice of those 58 drops, the intervening pages contain nothing but a long table and a graph. In the typescript that Millikan submitted to the journal (which seems not to have survived), this sentence presumably followed almost immediately after the statement qualifying it. Thus a careful reading of the context of Millikan’s words greatly diminishes their apparent significance as evidence of misconduct.

In fairness, I should acknowledge that when Millikan published his semi-popular book The Electron in 1917, he used verbatim the section of his 1913 paper on Stokes’s law, thus repeating the offending assertion of having reported every drop, without the earlier qualifying statement. Nevertheless, after reading The Electron, I came away with the impression that Millikan’s real rival was never the hapless Ehrenhaft. More likely, Millikan was trying to take on J. J. Thomson-not because they disagreed scientifically but because both men wanted to be remembered as the father of the electron.

Mishandling Minorities?

The notion that a Nobel laureate had cooked his data is so shocking that it would naturally enough attract the attention of journalists. But I suspect that Millikan has also been targeted by some historians of science because he was white, male and very much a part of the establishment. For example, there is a letter, noted in feminist circles, in which Millikan advised the President of Duke University not to hire a woman professor of physics. This correspondence dates from 1936, by which time Millikan was the head of the California Institute of Technology. W. P. Few, president of Duke, had written to Millikan in confidence, asking his advice. Millikan’s response shows his unease: “I scarcely know how to reply to your letter,” he begins. “Women have done altogether outstanding work and are now in the front rank of scientists in the fields of biology and somewhat in the fields of chemistry and even astronomy,” Millikan writes later, “but we have developed in this country as yet no outstanding women physicists.” He points out that “Fraulein Meitner in Berlin and Madame Curie in Paris” are among the world’s best physicists, but that’s Europe, not the U.S. “I should therefore,” he concludes his confidential advice, “expect to go farther in influence and get more for my expenditure if in introducing young blood into the department of physics I picked one or two of the most outstanding younger men, rather than if I filled one of my openings with a woman.”

In his private correspondence, Millikan also reveals an attitude toward Jews that would not be acceptable today. For example, writing from Europe to his wife, Greta, he describes physicist Paul Ehrenfest (not to be confused with Felix Ehrenhaft) as “a Polish or Hungarian Jew [actually Austrian] with a very short, stocky figure, broad shoulders and absolutely no neck. His suavity and ingratiating manner are a bit Hebraic (unfortunately) and to be fair, perhaps I ought to say too that his genial openmindedness, extraordinarily quick perception and air of universal interest are also characteristic of his race.”

What is one to make of these lapses? They are certainly not the rantings of a mindless bigot. Still, they reveal troubling biases, even if they were typical at that time of a man of his upbringing and background. But regardless of whatever prejudices Millikan harbored, they don’t seem to have interfered with his judgment of some excellent scientists. As mentioned, Lise Meitner, a Jewish woman, was in his view one of finest physicists alive. His hero at Chicago, A. A. Michelson, was also Jewish, as were many of the stars Millikan personally recruited to Caltech: Paul Epstein, Albert Einstein, Theodore von Karman and Beno Gutenberg, among others.

Such actions demonstrate that Millikan’s personality was more complex than his detractors acknowledge. Like anyone, he had his strengths and his flaws. He wasn’t generous enough to put his student’s interests ahead of his own at a critical point in his career. In describing the results of his oil-drop experiment, he let himself get carried away a bit in demonstrating the correctness of his empirical correction to Stokes’s Law. Also, his words about women and Jews grate on modern sensibilities. But Robert Andrews Millikan was not a villain. And he certainly did not commit scientific fraud in his seminal work on the charge of the electron.