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ARTHUR S / . KING [anomaly 18, 1876-April 1 7, 1 95 7 BY ROBERT B. KING ARTHUR SCOTT KING was born on January 18, 1876, in Jerseyville, Illinois, and diecl in Pasadena, California, on April 17, 1957. He was elected to the National Academy of Sciences in 1940. His father, Robert Andrew King, born in Missouri in 1830, was a clescenclant of Scottish-Irish from Northern {relancI who settled in Virginia in the eighteenth century and moved to Washington County, Missouri, in 1817. Arthur's mother, Miriam Munson King, came from a New Englanc! family that hac! emigrated from Lincolnshire, En- gland, in the seventeenth century. Robert Andrew King stucI- iecl law anti set up a successful practice in Union, Missouri. He also server! in the Missouri state legislature. During the Civil War, he moved his family to Jerseyville, Illinois, where he served as circuit judge for southern Illinois, sitting in Jerseyville. Arthur's older brother, Louis, was born in Jerseyville. Arthur was a rather frail boy and suffered from chronic asthma brought on, his parents believed, by the clamp cli- mate of southern Illinois. This was a major reason for the family's move to California in 1883. They purchased a small farm about five miles north of Santa Rosa, at the point 181

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82 BIOGRAPHICAL MEMOIRS where Mark West Creek emerges from the hills into the Santa Rosa plain. Robert Andrew set up a law office in Santa Rosa, com- muting by horse ant! buggy. The healthy California climate was effective, ant! Arthur was never again troubled with asthma; in fact, he was remarkably healthy the rest of his long life. Around IS90 the family moved to Fresno, where Arthur's father again set up an active law practice and Arthur attendee] the public schools. During the latter part of the nineteenth century, the great central valley of California was rapidly becoming the state's agricultural heart and Fresno the metropolis of the southern portion of the valley. A no- table event in King's life here, and one that he liked to recall in later years, was a pack trip with a group of Fresno men and boys into the Kings River Canyon. At that time, this was unclisturbed wiTct mountain country, now part of a national park. He attended the Fresno public schools, graclu- ated from Fresno High School in IS95, and was admitted! to the University of California (then only one campus) at Ber- keley. During his unclergracluate years at Berkeley, King be- came interested! in science, especially physics, in which he must have done well because on graduation in IS99, he was acimittec! to the graduate school in physics. At the beginning of the twentieth century, spectroscopy was becoming a major field of research in physics. No ad- equate theory yet existed to explain the lines observer! with a spectrograph when elements were heater} by flame, arc, or high-voltage spark. However, a great clear of ciata on mea- surement of wavelengths ant! estimated relative intensities of lines appearing in arc and spark spectra were being pub- lished. King was intrigued by this, and, fortunately, his re- search supervisor, Professor Percival Lewis, was interested in spectroscopy. King's first paper, published in the Astro- physicaliournal in 1901, was concerned with the structure of

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ARTHUR S. KING 183 the cyanogen bands (CN) as was his third paper (with Pro- fessor Lewis) in 1902. King's final examination for'the Ph.D. egree took place on May 8, 1903. His thesis was titled "The Structure of Arc Spectra and Some Effects of Changes in Physical Conditions." He was awarclecT his doctorate, the first Ph.D. in physics given by the University of California, which since then has probably proclucec3 more Ph.D.s in physics than any other American university. King was fortunate to receive a Whiting Fellowship for study abroad. The size of the fellowship is not known, but it was sufficient to enable him to spencl two years in the phys- ics laboratories of the universities of Bonn and Berlin, then the leaders in spectroscopic research, and to do consicler- able traveling in Europe as well. The majority of his time . . . . was spent in the laboratory of the leading spectroscopist of the time, Professor Heinrich Kayser, at Bonn. Kayser's Handbuch der Spectroscopy, continually revised, was the pri- mary source of ciata on wavelengths, estimated intensities, ant! identification of the spectral lines of the elements. In Kayser's laboratory King clesignecl and built his first electric furnace for excitation of the spectra of metals. It was clear to him that the furnace provider! a new range of controlled excitation fitting with the existing sequence of spectroscopic sources: flames, arc, and spark, between the flame ant! the arc. His first paper on the electric furnace was published in the Annalen der Physik in 1905. King's primary interests were in the changes in the spec- tra of the elements produced by different methods anti degrees of excitation. At that time, excitation was pretty well limited to the classic arc, spark, and flame sources. Of course, these showed quite different sets of spectral lines, which lee! to the distinction between spectra of neutral and ionizer! atoms of the metals. Obviously, a source capable of producing spectra under conditions of thermal equilibrium

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84 BIOGRAPHICAL MEMOIRS with controllable temperatures would be highly desirable. King returned to Berkeley as an instructor in physics in 1905. Two notable events in King's life occurred in 1906: one was a paper he published in the Anna1ten der Physik that described an electric furnace for spectroscopic purposes. This was the forerunner of the King furnace. The other was his marriage to Louise Burnett, the daughter of a Presbyte- rian minister and a descendent of early New England and New York families. The Kings had two sons, Robert, born in 90S, and Ralph, born in ~ 9 ~ ~ . In 1907 George E. Hale offered King a position on the staff of the recently established Mt. Wilson Observatory in Southern California. Hale, founder and first director of the observatory, was forming a staff of competent young men who were destined to dominate observational astronomy for many years. Hale was a strong believer in the need for an associated physical laboratory to provide data necessary for interpretation of astronomical observations, especially spectroscopic observations of the sun and stars for which the great telescopes located on Mt. Wilson were designed. Hale's remarkable enthusiasm was shared by the staff. He had the ability to pick good people, not only the scientific staff but the support people as well. He also felt that one of the main objectives of the observatory should be the under- taking of basic and extended research programs seldom undertaken by university researchers at that time because they depended on continued support over a long period of time and significant results were not expected to be forth- coming in a few months. This policy applied to both astro- nomical and physical laboratory programs. The large en- dowment (for the time) from the Carnegie Institution of Washington was able to provide continuing support for ma- jor projects such as the Mt. Wilson Observatory. At that

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ARTHUR S. KING 185 time there was no National Science Foundation, and finan- cial support of scientific research by the government came largely through private and state-supported universities. A physical laboratory as part of the observatory was one of Hale's several innovative policies. He had already set up a small laboratory on the mountain that soon proved to be impractical largely (lue to power limitations. It was also HaTe's idea that it would be best for the observatory staff to live in Pasadena rather than on Mt. Wilson. This also has proved to be a wise decision. Consequently, the laboratory was es- tablished in Pasadena in conjunction with the shops and offices of the staff. In 1908 Hale published an article in the Astrophysical Journal (lescribing a new physical laboratory being constructed for the observatory in Pasadena. At the time it was probably the best-equipped physical laboratory west of Chicago. In the same issue of the Astrophysical Journal containing HaTe's article was a paper by King describing a newly de- signed electric vacuum furnace for spectroscopic observa- tions. This was the furnace that became known as the King furnace. It remained basically unchanged during King's Tong series of spectroscopic observations extending over almost forty years. The heating element of the furnace was an accurately machined graphite tube about one-half inch in diameter inside with an eighth-inch wall thickness. The tube was cIampecl between graphite blocks, which in turn were held tightly in water-cooled metal clamps. The whole assembly was enclosed in a vacuum chamber with quartz windows at each end. Voltages in five volt stages between 5 and 50 volts provided high currents through the tube. The current was .. . . . . .. . . . ~ controlled by a rheostat, while the observer crutch cont~nu- ally monitor the temperature inside the tube by means of an optical pyrometer. Temperatures up to 3000C could be

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86 BIOGRAPHICAL MEMOIRS achieved, and almost any solic! substance could be melted or vaporized en c! most of its molecules dissociated. The incandescent vapor, when focused on the slit of a spec- trograph, produced emission lines, mainly those of the neutral atom. At high furnace temperatures, the molecular bands of C2 en c! CN became prominent. Absorption spectra could be observed by placing a graphite plug in the center of the furnace tube or by focusing the beam of light from a source of continuous spectrum such as a tungsten filament at the center of the heated tube, then onto the slit of the spec- trograph. The photographic plate homer was mounted on a horizontal track above floor level. The Pasadena laboratory was equipped with two large electrograting spectrographs. One had a plane grating in a 30-foot-focus, Litrow-type mounting. The second user] a con- cave grating of lL5-feet focus in a Rowlancl-type mounting. Both were mounter! vertically in a pit. This arrangement proviclecl more free floor space and excellent temperature stability. Most of King's work was done with the concave grating spectrograph. Ever since his European sojourn King hac! loved to travel. In 1914 he purchased a new Overianc! touring car, a power- ful meclium-size four-cylincler automobile, and began to ex- plore the local country. Almost every Sunciay he took his family for an afternoon ricle: to the beaches, the moun- tains, or just through the orange groves to a nearby town. He was the first Mt. Wilson staff member to cirive his family up Mt. Wilson. The oIcl toll roacI, while well maintainecl, was only one car wicle, except for frequent "turnouts' and for the inexperienced it was a real adventure. In 1915 King drove his family to Berkeley, where they spent most of the summer, and frequently visited the Pan American Tnterna- tional Exposition in San Francisco. He also took them to Lake Tahoe en c! to Sequoia National Park.

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ARTHUR S. KING 187 World War I did not seriously disrupt the observatory's research programs, although King and Harold D. Babcock spent some time developing an acoustical submarine-de- tecting device that seems to have been a forerunner of the sophisticated and very effective detection devices developed during World War IT. By 1918 the war had created a short- age of physics instructors at Berkeley, and King was asked to come and help teach. He obtained a leave of absence from the observatory and took his family with him to Ber- keley for several months. King lived most of his adult life during what this writer considers the golden age of Southern California, say, be- tween 1900 and the beginning of World War TI. The coun- tryside, originally semidesert, was beautiful, with the allu- vial slopes at the base of the mountains covered with citrus groves interspersed with attractive and prosperous small towns. The lower-lying portions of the river valleys were devoted to alfalfa fields and dairy and vegetable farms. Smog was not yet a problem, nor was overpopulation or traffic. In fact, Southern California was a delightful place to live and was appreciated by easterners and Midwesterners, who moved there in large numbers. Industry was mainly engaged in services and construction. Manufacturing was small scale and located mainly in east Los Angeles. It was a favorable atmosphere for scientific research; the observatory thrived and its neighbor, the California Institute of Technology, began its development into a great research institution, due in large part to the efforts of George E. Hale. Beginning in 1909 King developed his well-known tem- perature classification of spectral lines of the elements. His earliest publications indicate he had always been interested in the differences in the relative strengths of lines in a given spectrum with the degree of excitation. The graphite tube electric furnace made it possible to sort out lines that

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88 BIOGRAPHICAL MEMOIRS appeared at different known temperatures and strengths with increasing temperature and were therefore presum- ably associated with different energy levels in the atom. He thus proceeded to adopt an arbitrary scale of estimates of relative intensity of lines in a given spectrum and associate it with the temperature at which the lines appeared. The lines that appeared at the lowest temperatures usually be- Tow 2000 en cl strengthened rapidly with increasing tem- perature were clesignatecl Class T. Classes Il. TIT, and {V cles- ignate(1 lines appearing at increasingly higher temperatures. Class V inclucled lines that first appeared] at high tempera- tures but were much stronger in the arc spectrum. King's intensity estimates were meticulous and very consistent. These intensity estimates and the temperature classifications proved to be key ingredients in the later-term analyses of the com- plex spectra of the metals ant! rare earths. In nearly all of his observations over a periocI of almost forty years King usecI a concave grating spectrograph of 15-foot focus in a Rowlanc! mounting in a vertical rather than the usual hori- zontal arrangement. The grating was located in a pit that ensured quite constant temperature, ant! the plate hoIcler was mounted on a convenient horizontal track above floor level. Because of HaTe's interest in the magnetic splitting of the many lines observed in sunspot spectra, the laboratory acquirer! a large Weiss electromagnet capable of producing fields up to 30,000 gauss. King ant! others user! this to recorc! spark spectra of several metals and to measure the Zeeman splitting of many lines. In later years these data also proved useful and often conclusive evidence in the identification of the terms involved in transitions. However, of greater importance in the 1920s and 1930s to those involved in the term analysis of complex spectra were King's estimated in- tensities and temperature classifications of lines. They fur-

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ARTHUR S. KING 189 nished clues and often unique evidence about the ordering of the electronic energy levels in the atom. King continued this work throughout the 1920s en c] 1930s, in fact until his retirement. In the late 1920s King became interested in the spectra of the rare earth elements; accurate wavelength measurements had not been clone on many of them. The main reason for this was the difficulty in obtaining pure samples of these elements. Usually samples contained mix- tures of two or more rare earth elements, and consequently spectroscopic observations were discouraging. King contacted] a retired industrial chemist named McCoy who was making a hobby of purifying rare earths. McCoy's samples enables! King to make wavelength measurements, furnace arc, and spark intensity estimates as well as tem- perature classifications of their spectral lines. These data were basic to the term analysis of these very complex spec- tra. It is not too much to say that probably little wouIc! have been accomplished for a long time in the term analysis of rare earth spectra without King's data. King continued his observations of rare earth spectra until his retirement in 1943. The graphite tube furnace also led to the discovery of an important isotope. The furnace at higher temperatures brought out the band spectra of the characteristic molecules CN en c! C2 (CN because of resiclual air in the furnace en- closure). King had often recorded spectra of the CN bands and also the carbon bands called the Swan bands whose primary head lay in 4737 angstroms. This band had been identified as belonging to the cliatomic molecule C2. Fur- nace spectra at high temperature and Tong exposure showecl a much fainter but almost identical bancI heat! at \4744.5 with the resolved components degrading in intensity to- warc! the violet as dicl those associated with the strong X4737 band. The faint 4744.5 band hacl also been observed in the

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90 BIOGRAPHICAL MEMOIRS spectra of N-type stars, the co-called carbon stars. King had suspected for some time that these faint bands were prob- ably due to the presence of the isotope Cl3 forming with the dominant isotope c~2 the molecule Ci2C~3. Since the presence and relative strength of the 4744.5 band was con- sistent in the furnace spectra at high temperature, the iso- tope was probably stable (unlike the later-d~scovered iso- tope Cat. The theory of diatomic molecular spectra or band spectra was still in the process of development, and King invited one of those who was engaged in this work, R. T. Birge of the University of California, to collaborate. They published a paper in Nature announcing the discovery of the carbon isotope of mass 13. The comprehensive paper by King and Birge was published in 1930 in the Astrophysical journal. The position of the band head and the wavelength of the secondary lines matched exactly those predicted by theory for the molecule C~2C~3. This identification also, of course, solved the mystery of the presence of the faint band head in spectra of carbon stars mentioned above. During the :1930s King continued his observations of fur- nace spectra, particularly of the rare earths; in fact, he did so until his retirement. In 1936 he collaborated with his son, Robert, in developing a method using the graphite tube furnace for the quantitative measurement of the true relative strengths of lines in complex spectra. These data were desired by astronomers studying high-dispersion stel- lar and solar spectra. Thus, it can be said that the majority of King's work in the team was directed toward! providing data for astrophysical applications; his wavelengths, line in- tensity, and temperature classifications were essential ingre- dients to the term analyses of complex spectra, which were necessary for interpretation of solar and stellar spectra. in ~ 941 King served as president of the Astronomical Society of the Pacific, one of the oldest astronomical societ-

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ARTHUR S. KING 191 ies. He also served a term as president of the American Meteorical Society in the 1930s. King retired in 1943 and soon became involved with war work at CalTech, where he joiner! a project concerned with the underwater ballistics of aircraft torpedoes. He contin- ucc! with this work for several years after the end of the war when the project was taken over by the U.S. Navy but re- mained in Pasadena. Good health hacl been as asset to King since his early youth and permitted him to remain active Tong after retire- ment. However, in the mict-1950s he overextended himself on an automobile trip with his wife to Oregon ant! never really recovered his full strength. His health failed rapidly in 1957, and he passed away in his sleep on April 25th in Pasadena. He left his wife, two sons, and four granciciaugh- ters.

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192 BIOGRAPHICAL MEMOIRS SELECTED BIBLIOGRAPHY Uber Emissionsspektra von Metallen im Electrichen Ofen. Ann. Phys. (Leipzig) 16:360. An electric furnace for spectroscopic investigations. Astrophys. /. 28:300. Furnace spectra in hydrogen atmosphere (Ca, Cs, Cu. Fe, Hg, Na). Astrophys. J. 27:353. Effect of pressure upon electric furnace spectra of Cr. Fe, & V. Astrophys. J. 4:37. The occurrence of the enhanced lines of titanium in furnace spec- tra. Astrophys. J. 37:119. Some electric furnace experiments on the emission of enhanced lines of Ti in a hydrogen atmosphere. Astrophys. f. 40:213. The properties in the electric furnace of the banded spectra as- cribed to titanium oxide, magnesium hydride, & calcium hydride. Astrophys. J. 43:341. A study of the relation of arc & spark lines by means of the tube arc (Ca, Fe, Ti, V). Astrophys. J. 38:315. The tube-arc spectra of iron & a comparison of dissymetries in spark spectra. Astrophys. f. 41 :373. Discussion of some evidence on the origin of radiation in the tube resistance furnace. Astrophys. i. 49:48. On the separation in the magnetic field of some lines occurring as doublets & triplets in sun-spot spectra (Fe, Ti) Astrophys. J. 29:76. The Zeeman effect for titanium. Astrophys. f. 30:1. The correspondence between Zeeman effect & pressure displace- ment of spectra of iron, chromium, & titanium. Astrophys. f. 31:433. The influence of a magnetic field upon the spark spectra of iron & titanium. Astrophys. J. 34: 225. The structure of the lithium line \7608 & its probable occurrence in the sun-spot spectra. Astrophys. J. 44:169. With E. Carter. Preliminary observations of the spectral calcium & iron produced by cathodo-luminescence. Astrophys. f. 44:303. With E. Carter. A further study of metallic spectra produced in high vacua (Ca, Cd, Fe, Mg, Mn, Ti). Astrophys. f. 49:224. The electric furnace spectrum of iron in the ultra violet, with data for the blue & violet. Astrophys. f. 56:318. Electric furnace spectrum of scandium. Astrophys. jr. 54:28.

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ARTHUR S. KING 193 Electric furnace spectrum of titanium in the ultra-violet. Astrophys. [. 50:135. Experiments of the possible influence of potential difference on the radiation of the tube resistance furnace. Astrophys. f. 52:187. Intensity differences in furnace & arc among the component series in band spectra. Astrophys. f. 53:161. Lines of tungsten & rhenium appearing in the spectrum of the electric furnace. Astrophys. f. 75:370. Observations of the Zeeman effect for electric furnace spectra. Astrophys. [. 51:107. Spectroscopic phenomena of the high-current arc. Astrophys. f. 64:239. Temperature classification of the spectra of europium, gadolinium, terbium, dysprosium, & hafnium. Astrophys. f. 72:221. Temperature classification of the stronger lines of cerium & praseody- mium. Astrophys. J. 68:104. Temperature classification of the stronger lines of columbium, with notes of their hyperfine structure. Astrophys. f. 73:13. Temperature classification of the spectrum of neodymium. Astrophys. J. 70:9. Temperature classification of infrared iron lines. Astrophys. J. 80:124. Temperature classification of samarium lines. Astrophys. f. 82:140. With R. B. King. Relative gf values for lines of FeI from electric furnace absorption spectra. Astrophys. J. 82:377. A spectroscopic examination of meteorites. Astrophys. f. 81:507. With R. B. King. Relative gf-values for lines of FeI and TiI. Astrophys. J. 87:24. The spark spectrum of iron, \~5016-7712, with identification of FeII lines in the solar spectrum. Astrophys. f. 87:109. With H. N. Russell. The arc spectrum of europium. Astrophys. f. 90:155. Temperature classification of gadolinium lines. Astrophys. f. 97:323.

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