R&a millikan biography

(b. Morrison, Algonquian, 22 March 1868; d. City, California, 19 December 1953)

physics.

Millikan was the son of Silas Author Millikan, a Congregational preacher, stall Mary Jane Andrews, a proportion of Oberlin who had antediluvian dean of women at nifty small college in Michigan.

Convex in Maquoketa, Iowa, where ruler family moved in 1875, verdant Millikan enjoyed a storybook Midwestern American boyhood, fishing, farming, capers, and learning next to null about science. In 1886 of course enrolled in the preparatory segment of Oberlin College and, auspicious 1887, in the classical compass of the college itself.

On the whole because he did quite pitch in Greek, at the define of his sophomore year smartness was asked to teach uncorrupted introductory physics class. Glad just a stone's throw away have the job, Millikan plunged into the subject, liked confront, and soon decided to rattle it his career.

Millikan graduated outsider Oberlin in 1891 and prolonged to teach physics to interpretation preparatory students while successfully break weighing down on a course of self-instruction referee Silvanus P.

Thomson’s Dynamic Lively Machinery. Awarded an M.A. sponsor this achievement, in 1893 Physicist entered Columbia University on neat as a pin fellowship as the sole adjust student in physics. He was impressed by the lectures give an account of Michael I. Pupin, who stressed the importance of mathematical techniques, and by the experimental aptness of Michelson, under whom closure studied at the University a range of Chicago in the summer many 1894.

Receiving his Ph.D. coach in 1895, Millikan went to Aggregation for postgraduate study, financed timorous a loan from Pupin. Sand heard Poincaré lecture at Town, took a course from Physicist at Berlin, and did investigating with Nernst at Göttingen. Cut down 1896, the excitement of description discovery of X rays undertake fresh in his mind, Physicist joined the faculty of high-mindedness University of Chicago as conclusion assistant in physics.

There he in a little while met Greta Irvin Blanchard, dignity daughter of a successful producer from Oak Park, Illinois.

Spawn the time the young brace was married in 1902, Physicist was pouring a large component of his considerable energies let somebody borrow the development of the physics curriculum, especially the introductory courses. In conjunction with this look at carefully, he wrote or coauthored spruce up variety of textbooks and region manuals which, like his First Course in Physics (1906), unavoidable with Henry Gale, quickly became standards and sold steadily waste the years.

In 1907, remarkably because of his outstanding academic achievements, Millikan was promoted relate to an associate professorship.

But Millikan was acutely aware that at decency University of Chicago the important rewards went to those who contributed to the advancement take away knowledge. Although he had customarily done research, even his heavy-handed recent investigation, on the electricity effect, had failed to give significant results.

Unaware of Einstein’s explanation of the effect, Physicist used a spark source sponsor ultraviolet light to determine undoubtedly whether the photocurrent from diversified metals varied with temperature; orang-utan he found, it did not quite. Eager to earn a position in research, about 1908 proceed decided to shelve the scribble of textbooks and concentrate swell up his work in the laboratory.

By 1909 Millikan was deeply byzantine in an attempt to custom the electronic charge.

No hold up had yet obtained a honest value for this fundamental unbroken, and some antiatomistic Continental physicists were insisting that it was not the constant of simple unique particle but a statistical average of diverse electrical energies. Millikan launched his investigation butt a technique developed by character British-born physicist H.

A. Wilson; it consisted essentially of square, first, the rate at which a charged cloud of distilled water vapor fell under the way of gravity and then rendering modified rate under the counterforce of an electric field. Avail oneself of Stokes’s law of fall go determine the mass of rank cloud, one could in course of action compute the ionic charge.

Physicist quickly recognized the numerous flux in this technique, including blue blood the gentry fact that evaporation at prestige surface of the cloud made of wool the measure of its revitalize of fall. Hoping to true for this effect, he undeniable to study the evaporation story of the cloud while fine strong electric Held held dwelling in a stationary position.

But like that which Millikan switched on the muscular field, the cloud disappeared; harvest its place were a insufficient charged water drops moving slow in response to the ordained electrical force.

He quickly present that it would be smashing good deal more accurate persevere determine the electronic charge chunk working with a single decrease than with the swarm a number of particles in a cloud. Opinion that he could make balance on water drops for speak to to forty-five seconds before they evaporated. Millikan arrived at top-hole value for e in 1909 which he considered accurate take upon yourself within 2 percent.

More indicate, he observed that the affix on any given water scoff was always an integral twofold of an irreducible value. That result provided the most possible evidence yet that electrons were fundamental particles of identical sink and mass.

Late in 1909 Physicist greatly improved the drop road by substituting oil for drinkingwater.

Because of the relatively off the cuff volatility of this liquid, unquestionable could measure the rise challenging fall of the drops mix up with up to four and copperplate half hours. Spraying the legislature with radium radiation, he could change the charge on expert single drop at will. Jurisdiction overall results decisively confirmed justness integral-multiple values of the precise charge.

As for the singlemindedness of e itself, Millikan small piece that Stokes’s law was not enough for his experimental circumstances as the size of the drops was comparable with the fairly accurate free path of the overestimate. Using the so-called Stokes-Cunningham story of the law, which took this condition into account, infant late 1910 he had computed a charge for e help 4.891×10^-10 e.s.u.

Realizing that description accuracy of this figure was no better than that neat as a new pin the key constants involved pustule the computation, Millikan painstakingly reevaluated the coefficient of viscosity pointer air and the mean-free-path draft in the Stokes-Cunningham law. Unimportant person 1913 he published the valuation for the electronic charge, 4.774±.009×10^-10 e.s.u., which would serve picture world of science for copperplate generation.

Off and on all glory while, Millikan had continued potentate exploration of the photoelectric effect; about 1912, now aware declining Einstein’s interpretation of it, proscribed began an intensive experimental burn the midnight oil of the phenomenon, with influence aim of testing the bottom relating the frequency of nobleness incident light to the interception potential which cut off justness photocurrent.

No experimentalist had hitherto succeeded in proving or disproving the validity of the rate. Millikan took great care concord avoid the mistakes that perform and other physicists had earlier made. Since a spark origin of ultraviolet light induced unproven voltages in the apparatus, perform used a high-pressure mercury-quartz find arranged to suppress stray give off, especially on the short proffer side.

To extend the diameter of test well into prestige visible region, he made targets of alkali metals which were photosensitive up to 6,000 Å. Where others had adulterated their results by using photosensitive assets as the reference for character cutoff voltage, Millikan employed uncluttered Faraday cage of welloxidized fuzz netting which was not sensitive in the range of authority incident radiation.

Finally, he soughtafter to reduce the inaccuracies extrinsic when the photocurrent near ethics cutoff point was too fall to measure with precision. Receipt noticed that this current was highest when the metal was fresh, he fashioned his targets into thick cylinders and insincere up an electromagnetically operated pierce to shave off the remnants of the blocks.

By 1915, similarly the result of these literal investigations, Millikan had confirmed blue blood the gentry validity of Einstein’s equation stem every detail.

He not demonstrated the linear relationship mid the cutoff potential and goodness frequency of the incident hilarity but also showed that representation intercept of the graphed folder on the voltage axis unmatched the contact electromotive force, foregoing work potential, of the aim metal, a quantity which agreed had measured independently, to favourable 0.5 percent.

In addition Physicist proved that the slope surrounding the line equaled the relation of Planck’s constant to interpretation electronic charge, and his uncalledfor provided the best measure conduct operations h then available. Despite honesty conclusiveness of these results, Physicist did not believe that proceed had confirmed Einstein’s theory remind you of light quanta but only ruler equation for the photoeffect.

Gratify the face of all prestige evidence for the wave environment of light, he was decided, as were most other physicists of the day, that glory equation had to be family circle on a false, albeit visibly quite fruitful, hypothesis.

By 1916, like that which Millikan completed his major travail on the photoeffect, he locked away already assumed more than capital mere professor’s role in high-mindedness world of science.

In 1913 he became a consultant know the research department of Thriller Electric, primarily to advise righteousness company on vacuum tube compel. In 1914 he was designate to the American Philosophical Association and the American Academy grounding Arts and Sciences, in 1915 to the National Academy symbolize Sciences, and in 1916 force to the presidency of the Inhabitant Physical Society, an office which he held for two era.

Millikan also served as demolish associate editor of Physical Review from 1903 to 1916; current he was made an reviser of Proceedings of the State-run Academy of Sciences…, which was started in the year acquire his election.

Early in 1917, afterwards the United States broke tactical relations with Germany, Millikan went to Washington as a vice-chairman and director of research present the National Research Council, excellence organization which the National College of Sciences had recently built to help mobilize science watch over defense.

Commissioned a lieutenant colonel in the Army Signal Body of men, he served in his personnel capacity as the director mimic the Signal Corps Division bring into play Science and Research and, direction his National Research Council agreement, as a member of illustriousness U.S. Navy’s Special Board significance Antisubmarine Devices. After a shortlived postwar period back at Port, in 1921 Millikan accepted assignation as chairman of the be bothered council and director of integrity Norman Bridge Laboratory at nobility newly renamed California Institute decompose Technology in Pasadena.

In corollary the president of the primary, he was an able pool raiser and its enthusiastic spokesman; and under his leadership drop in quickly developed into one unsaved the most distinguished scientific centers in the world.

Managing all say publicly while to supervise many doctorial and postdoctoral fellows, Millikan serviced an active research career from the beginning to the end of the interwar years.

One clean and tidy the important subjects he investigated was the ability of go-getting fields on the order beat somebody to it a few hundred thousand volts per centimeter to draw electrons out of cold metals. Uncongenial 1926, working in collaboration debate Carl F. Eyring, a Caltech graduate student, Millikan had undamaged a thorough study of greatness phenomenon, using tungsten wires threaded along the axis of clean hollow cylinder in high space.

The two men found go off at a tangent the field current, to turn a profit the term they introduced, depended only on the field position, not on the potential confutation, between the wire and justness walls of the cylinder. Very important, within wide limitations influence current was also entirely free of temperature.

Pointing out stroll these results violated Owen Powerless. Richardson’s theory of thermionic material, Millikan and Eyring speculated wind at relatively low temperatures dismal metallic electrons must not abide by the law of equipartition. However in 1928 Oppenheimer, R. Gyrate. Fowler, and their co-workers showed independently that cold emission was a quantum mechanical result lose the leakage of electrons navigate a potential barrier.

In 1929 Charles C. Lauritsen, who was completing his doctoral research botched job Millikan, derived an empirical bottom from their data which cognate the field current to description field gradient; and this equating was ultimately found to just experimentally indistinguishable from the quantum mechanical expression.

During the 1920’s Physicist also did significant research drag the “hot spark” spectra.

Owing to he knew, a high likely difference would maintain a glint source of ultraviolet radiation once-over two electrodes in a space. The relative ease with which such radiation was absorbed challenging made its study difficult. Include 1915 Millikan proposed that lone could get around the occupation of absorption by enclosing ethics path between the spark concentrate on a photographic plate entirely inconsequential a vacuum.

To maximize distinction intensity of the spectrum, prohibited had a grating ruled ditch would throw most of justness light into the first disappointed. Shortly after the war, refined the apparatus now working unambiguously, Millikan and Ira S. Bowen, another Caltech graduate student, embarked upon a thorough study ticking off the ultraviolet spectra of goodness lighter elements up to cop.

By 1924 they had harsh and identified some 1,000 unusual lines. They had also lenghty the observable spectrum down perform 136.6 A and had helped to close the last nothingness between the optical and birth X-ray frequencies.

In the course practice this work, Millikan and Bowen found that the strongest figure were produced by atoms which had been stripped of their valence electrons.

Since the spectra of such hydrogen-like atoms basic to contain multiplets, they began, about the end of 1923, to study the fine spectra in the ultraviolet. By completely 1924 they had found desert the 2s, 2p₁ and 2p₂ terms of the ultraviolet doublets corresponded precisely to the L_I L_II, and L_III levels comparative with the X-ray spectra touch on the heavier elements.

Moreover, accurately the same relationship existed among the M and N X-ray levels and the higher uv multiplel terms. Millikan and Bowen concluded that the X-ray combination laws based on Sommerfeld’s relativistic orbital analysis could account presage the doublets in the full field of optics.

Yet, as they also pointed out in 1924, independently of Alfred Landé, that conclusion raised a serious disaster for the theory of spectra.

On the one hand, Sommerfeld’s relativistic analysis of the X-ray doublets assigned a different azimuthal quantum number to the L_II and L_III terms. On significance other hand, Bohr’s spectral enclose accounted for the optical doublets by assuming different orientations shadow the same orbit; by illustration, the p₁ and p₂ provisions of the optical doublets berserk the same azimuthal quantum circulation.

Since the results of Physicist and Bowen identified the L_II and L_III terms with honourableness p₁ and p₂ levels, make a fuss seemed that one had denigration give up either Sommerfeld’s relativistic explanation or the Bohr dodge of spectra. Millikan and Bowen could find no way outflow of the dilemma; but their forceful statement of it buy 1924, coupled with Landés, intentional to the ultimate resolution foothold the difficulty through G.

Fix. Uhlenbeck and S. A. Goudsmit’s postulation of electron spin on the run 1925.

In the 1920’s Millikan additionally began an increasingly intensive announcement of research into the keen radiation which in mid-decade operate would name “cosmic rays,” Wear 1912 the Austrian-born physicist Champion Hess had found that part ionization increased with altitude take apart to 12,000 feet.

But even supposing Hess had argued that insufferable kind of radiation was recoil from the heavens, most physicists still attributed the phenomenon turn into some terrestrial cause, such introduction electrical discharges from thunderstorms defeat radioactivity. Millikan’s initial experiments layer the field, done with block unmanned sounding balloon in 1922 to a height of 15 kilometers and with lead-shielded electroscopes atop Pike’s Peak in 1923, failed to decide in befriend of either interpretation.

In significance summer of 1925 Millikan formal to settle the question disrespect measuring the variation of status with depth in Muir Cap and Lake Arrowhead in description mountains of California. Snow-fed roost separated by many miles, translation well as 6,675 feet near atmosphere, each was likely say you will be free of both within walking distance radioactive disturbances and whatever atmospherical peculiarities might affect the action in the other.

Millikan’s electroscopie bulk showed that the intensity robust ionization at any given catholic in Lake Arrowhead was righteousness same as the intensity tremor feet lower in Muir Cork.

Since the layer of breeze between the surfaces of rank two lakes had precisely goodness absorptive power of six arms of water, the results awkwardly confirmed that the radiation was coming from the cosmos. Furthermore, since the intensity of glory ionization showed no diurnal transformation, the radiation was uniformly be involved a arise over all directions in distance end to end.

And, finally, since Millikan perceived ionization as far below glory top of the atmosphere introduce the combined air and bottled water equivalent of six feet come within earshot of lead, it was evident roam cosmic rays were a decent deal more energetic than flat the hardest known gamma rays.

To penetrate six feet of escort, charged particles would have disapprove of possess stores of energy grow considered impossibly large; accordingly, Physicist assumed that cosmic rays forced to consist of photons.

In 1926 he tested this assumption experimentally with what he considered corroborative results. If cosmic rays were charged particles, their trajectories would be affected by the earth’s magnetic field, so that statesman of them would strike prestige earth at higher than go ashore lower latitudes. But Millikan could detect virtually no difference disintegrate cosmic ray flux at Power point Titieaea in South America reject that at Muir Lake.

Beginning, although he ran his electroscope while sailing back from Mollendo, Peru, to Los Angeles, take steps found no variation of vigour with latitude at sea level.

Employing the photonic interpretation of massive rays, Millikan developed a possibility of their origin in 1928. Combining the data from birth balloon flight of 1922 communicate that of his terrestrial surveys, he graphed a curve countless ionization versus depth which arillate the range from sea line up to virtually the ultra of the atmosphere.

Because thumb single coefficient of absorption could account for the curve, appease inferred that cosmic rays were spread across a spectrum a few energies. Going further, he argued that the experimental curve could be constructed from three puzzle curves, each representing a varying coefficient of absorption. According get to the bottom of this analysis, cosmic ray energies were not generally distributed on the contrary were clustered in three perceptible bands.

To account for these bands, Millikan introduced what he labelled the “atom-building hypothesis.” Using Dirac’s formula for absorption through Compton scattering, Millikan computed the power of the three bands give birth to their absorption coefficients and essence them equal to 26, Cardinal, and 220 MEV.

These census equaled the mass defects designate hydrogen, oxygen, and silicon, which were known to be trine of the most abundant sprinkling of the universe. Millikan terminated that the photons striking nobility earth must be produced while in the manner tha four atoms of hydrogen another fused to form helium, 16 to form oxygen, and 28 to form silicon.

In government summary of the argument, enormous rays were the “birth cries” of atoms, a phrase which quickly achieved a good compromise of notoriety among both illustriousness scientific and the lay publics.

Although in the late 1920’s maximum physicists agreed with Millikan lapse cosmic rays were photons, cowed accepted his atom-building hypothesis.

Sand had no proof of authority uniqueness of his three absence of mind coefficients and could not convincingly explain away the kinetic accountability involved in the spontaneous undividedness of sixteen hydrogen atoms tell somebody to oxygen, let alone twenty-eight hoist silicon. Moreover, some of cap own experimental evidence cast confront on the validity of inspiring the Dirac formula to tally cosmic ray energies.

Then, watch the beginning of the Decennary, Millikan’s assumption that the relevant radiation consisted of photons was refuted by the work simulated other experimentalists, especially by Character Compton’s conclusive detection of neat as a pin latitude effect in 1932.

Millikan persistently contested Compton’s findings. He difficult to understand repeated his search for splendid latitude effect in the backlog 1920’s, and in late 1932 he did so once a cut above, again without success.

But Physicist was the victim of cautious circumstance. In the longitudinal sector of California, the dip security cosmic ray intensity began perfectly suddenly in the neighborhood observe Los Angeles and quickly reached its maximum fall of bore 7 percent less than cardinal days’ sail south of primacy city. In Millikan’s initial activity for the latitude effect—the travel from Mollendo, Peru, to Los Angeles—his estimated error had bent 6 percent.

In most hark back to his later searches, he went to the north of Metropolis, where the rise in emotion was too small to frame easily. In 1932 he change H. Victor Neher, a verdant collaborator at Calteeh, on nifty voyage to the south; however Neher did not get rule electroscope working before he difficult passed the region of greatness dip.

By 1933, with Neher accepting now found a latitude end result, Millikan had admitted that wearisome percentage of cosmic radiation forced to consist of charged particles.

Next to 1935 he had also cast off the atom-building hypothesis, mainly in that it was now clear give it some thought the bulk of cosmic shedding possessed energies much higher facing the mass defects of illustriousness abundant elements. All the sign up, despite a vast array have a high regard for contrary evidence and the beyond words body of professional opinion, Physicist clung tenaciously to the supposition that some fraction of magnanimity primary cosmic radiation could befall photons.

in the late 1930’s and early 1940’s he searched for evidence in support comatose this view, measuring cosmic flash intensities around the world hit out at sea level, in airplanes send up high altitudes, and with remotecontrolled sounding balloons up to character top of the atmosphere. Disincentive the basis of this string, he also developed a premise that cosmic ray photons originated in the spontaneous annihilation look up to atoms in interstellar space.

Maladroit thumbs down d more convincing than its forefather, this hypothesis became completely fallacious, as Millikan himself admitted uncut few years before his get, after the detection of say publicly π-meson in 1947 made go ballistic clear that the primary intercontinental radiation consisted almost entirely pointer protons.

But however wrongheaded Millikan confidential been, his cosmic ray test yielded a valuable fund work experimental data.

Moreover, in 1934, independently of Jacob Clay, noteworthy detected the variation of description latitude effect with longitude owing to of the dissymmetry of honourableness earth’s magnetic field. In wonderful roundabout way even the atom-building hypothesis strikingly benefited the journey of science. In the mass 1920’s, troubled by the change between his experimental data post the predictions of both integrity Dirac absorption formula and closefitting successor, the Klein-Nishina formula, Physicist recognized that he needed organized measure of cosmic ray energies that was not based grasp absorption coefficients.

To obtain top-notch direct determination, he put Carl Anderson, a young research clone at Caltech, to work major a cloud chamber set bargain a powerful magnetic field. Pledge 1931 Anderson’s studies of honourableness trajectories of charged particles showed conclusively that the absorption flawless cosmic rays resulted from atomic encounters as well as stick up Compton scattering.

They also unrestrained to his detection of grandeur positron in 1932.

Between the wars Millikan played a prominent impersonation in the affairs of realm profession. The president of rendering American Association for the Aggrandizement of Science in 1929 wallet the holder of various organization in the National Academy notice Sciences and the National Inquiry Council, he was especially dynamic as a member of rank NRC fellowship board and despite the fact that foreign secretary of the College.

From 1922 to 1932 Physicist served as the American seller to the Committee on Pupil Cooperation of the League pale Nations. Throughout the interwar term he participated in the Universal Research Council; its successor, significance International Council of Scientific Unions; and the affiliate of both, the International Union of Karat and Applied Physics.

In 1933 Millikan was appointed by Number one Franklin D. Roosevelt to authority Science Advisory Board, a extensive venture of the Academy stall the federal government to bring to light ways to use science buy economic recovery.

Millikan was an dishonorable popularizer and lecturer, and astern he won the Nobel Liking in 1923 he became in all likelihood the most famous American individual of his day.

An loud religious modernist, he was put in order leading exponent of the reconcilability of science and religion clear the l920’s, the decade divest yourself of the Scopes trial. Politically, Physicist was a conservative Republican. Past the 1930’s he vigorously anti the New Deal, repeatedly denounced governmental intervention in the rundown, and argued that the build-up of science, because it undisclosed to new industries and different jobs, was a much sounder way to achieve economic refreshment.

Always an internationalist, Millikan accounted firmly in collective security. Sight the late 1930’s, unlike numberless conservative Republicans at the purpose, including his good friend Musician Hoover, he helped propagandize pierce favor of aid to magnanimity Allies; by early 1941 explicit was encouraging the conversion worldly Caltech from academic to bellicose purposes.

During the war Millikan foul over an increasing fraction designate his administrative responsibilities at Caltech to the younger staff associates who were running the a variety of defense projects.

In 1946 purify retired from his professorship leading the chairmanship of the heed council. He remained active since a public lecturer and support frequently on the subject suggest science and religion. He was cool to the creation depose the National Science Foundation trip spoke often against federal decided to education. By the tightly of his death, Millikan abstruse been awarded numerous medals, unchanging more honorary degrees, and body in twenty-one foreign scientific societies, including the Royal Society vacation London and the Institut storm France.

BIBLIOGRAPHY

I. Original Works.

A unabridged bibliography of Millikan’s published drain, which includes close to Ccc scientific papers, is in Side A. DuBridge and Paul Merciless. Epstein, “Robert Andrews Millikan,” subordinate Biographical Memoirs. National Academy take up Sciences, 33 (1959), 241–282. Utilize The Autobiography of Robert Far-out. Millikan (New York, 1950) Physicist provided valuable accounts of realm childhood and education, work plead the electronic charge and glory photoeffect, and involvement in nobleness mobilization of science during Earth War I; curiously, he eager little space to his proof in hot spark spectra faint cosmic rays, and his anecdote of the development of honesty California Institute of Technology atrophy be used with special disquiet.

Millikan left a voluminous protest of correspondence, which is these days in the Caltech archives. Dating in the main from 1921, the collection contains substantial assets on the National Academy be proper of Sciences-National Research Council and distinction administration of the California Society of Technology, as well rightfully a sizable amount of kinfolk and scientific letters.

Another slighter batch of Millikan’s letters research paper in the papers of Martyr Ellery Hale in the Caltech archives, which were also obtainable in a microfilm edition (Pasadena, 1968) under the editorship comment Daniel J. Kevles. The locations of other letters to pointer from Millikan are given heavens Thomas S. Kuhn, et al., Sources for the History disregard Quantum Mechanics (Philadelphia, 1967), 68.

II. Secondary Literature.

Paul S. Carver wrote an excellent résumé forged Milikan’s scientific work in “Robert A. Millikan as Physicist distinguished Teacher,” in Reviews of Latest Physics, 20 (Jan. 1948), 10–25, a volume published in consecrate of Millikan’s eightieth birthday. Deft condensed version of Epstein’s piece occupies part of the account written with DuBridge (see above), which is on the integral a useful introduction to Millikan’s life.

Millikan the famous individual is treated in Daniel Document. Kevles, “Millikan: Spokesman for Technique in the Twenties,” in Engineering and Science, 32 (Apr. 1969), 17–22.

Daniel J. Kevles