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Biographical Memoirs: Volume 53 (1982)

Chapter:Ira Sprague Bowen

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Suggested Citation:"Ira Sprague Bowen." National Academy of Sciences. 1982. Biographical Memoirs: Volume 53. Washington, DC: The National Academies Press. doi: 10.17226/576.
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IRA SPRAGUE BOWEN December 21, 1898-Februa7:y 6, 1973 BY HORACE W. BABCOCK IRA SPRAGUE BOWEN was one of the outstanding physicists and astronomers of the twentieth century. He was giftec! with exceptional physical insight and with a compelling con- cern for funciamentals from which he seldom permitted him- self to be divertecI. As a pioneer in ultraviolet spectroscopy he discovered, with R. A. Millikan, evidence that led to the con- cept of electron spin in the vector mode] of the atom. He solver! the long-standing mystery of the "nebulium" lines in the spectra of gaseous nebulae, showing that they were "for- bidden" lines of ordinary elements. He was a master of ap- plied optics who was responsible for successful completion of the 200-inch Hale Telescope and for many ingenious crevices or optical systems that contributed enormously to mankincl's observations of the universe. Bowen was director of the Mount Wilson and Palomar Observatories for eighteen years. Here he took the leacI in developing a major organization for research and education while at the same time closely supervising details of observa- tory operations. On a wider scale, he accomplishecI much to broaden the opportunities for astronomers generally and to increase the number and efficiency of astronomical facilities. FAMILY BACKGROUND AND SCHOOLING The Bowen family traces its beginning in New England to Richard Bowen, who left Wales and settlecI in Rehoboth, 83

84 BIOGRAPHICAL MEMOIRS Massachusetts in 1643. During the Revolutionary War some members of the family were Tories and were forced to emi- grate to Canada. Later they returned to Washington County, New York. Ira Bowen's great-grancifather, Aaron Bowen, pioneered! in Steuben County, in the western part of the state. His grandfather, William H. Bowen, grew up on a farm in this region and married Juliza Cotton, whose family was I-ikewise of New England origin and had pioneered in the same section of the state. After spending his early years on the farm, Tra's father, lames H. Bowen, received his educa- tion at the local high school and at the Geneseo State Normal. He then became a preacher in the Wesleyan Methodist Church, a small denomination with fundamentalist doctrines and strict codes of conduct. James Bowen married Philinda Sprague, who tract grown up in the same rural community of Haskinsville in Steuben County and hacl completed her edu- cation at the Geneseo State Normal. Ira was born December 2l, IS98 at Seneca Falls, New York, where his father was at the time pastor of the local church. Two years later the family, including Ira's older brother, Ward, moved to MilIview, a small village in Sullivan County, Pennsylvania. While Tra was quite young, his father became business agent of the Wesleyan Methodist Church; the resulting responsibilities required frequent moves be- tween Houghton and Syracuse, with the result that from 1905 to 1908 Tra dicI not attend school but was taught at home by his mother, who was a licensed teacher in New York State. Following the death of his father in 190S, the boy's education was continued at Houghton Wesleyan Methodist Seminary, where his mother had obtained a position as a teacher. She later became principal of the high school department. During his high school years, Ira (or Ike, as he was known to his friends) took considerable interest in popular science as represented by Popular Mechanics and Scientific American. He

IRA SPRAGUE BOWEN 85 also played with lenses, wires, and batteries to the extent permitted by the very limitecI family finances. He graduated from the high school in 1915 as valedictorian of a class of seventeen. The first three years of Ike Bowen's college courses were in the junior college that formed part of Houghton Sem- inary. All of the courses in mathematics, physics, ant! astron- omy were taught by the president, I. S. Luckey, who was a most effective teacher and who was largely responsible for the unusually high scholastic standarcis at the school. For these three years Bowen had charge of the laboratory of the high school physics course; the income earned in this way was used to pay his tuition. His early interest in science deepenecI cluring Bowen's first college years. It was no doubt stimulatecI by the ingenuity requires! to devise suitable experiments with the limiter] equipment available, as well as by the formal courses. Follow- ing a connection establishecl by Luckey, Bowen transferred to Oberlin College for his senior year and received the A.B. degree in June 1919. While at Oberlin he came under the direction of Professor S. R. Williams, whose sympathetic col- laboration with his students in research projects was respon- sible for the continuation of many of these students in ad- vancec! stucly anct research. In a project of this sort, Bowen stucliecI the magnetic and magnetomechanical properties of samples of manganese steel supplied by Sir Robert HacIfield, with whom he eventually publishecI the results in the Proceed- ings of the Royal Society. During this year he also assisted in one of the general physics laboratories and gave some time to the Students Army Training Corps, in which he had enlisted before the end of World War I. In the fall of 1919, having been awarded a scholarship, Bowen took up graduate studies at the University of Chicago. In the two years that he remained there he attenclecl all of the

86 BIOGRAPHICAL MEMOIRS very comprehensive group of courses given by A. A. Michel- son on classical physics and R. A. Millikan on modern physics, as well as many other courses in the department. These con- tacts, and the involvement in a major physics department during a period of extraordinary progress, undoubtedly had a deep and lasting influence. In later life Bowen insisted that research should be aimed incisively at a welI-defined, funda- mental problem; he was intent on understanding the basic physics and had little patience with mere data-gathering pro- grams, which he characterized as "weather-bureau-type" . . activity. RESEARCH AND TEACHING At about the time of Bowen's arrival at the University of Chicago, Millikan's laboratory assistant, Dr. Ishida, an- nounced his intention of leaving the University and return- ing to Japan. Bowen immediately accepted the offer of this position, which he took up on January I, 1920. His first duties were to assist Tshida in the completion of his mea- surement of the viscosities of several gases by the oil-drop method. Upon Ishida's departure, however, Bowen was transferred to spectroscopic studies in the extreme ultraviolet using the vacuum spectrograph that had been developed by R. A. Sawyer and G. D. Shallenberger under Millikan's direction. At about this time significant improvements were introduced in the methods of ruling diffraction gratings, permitting extension of the shortward limit observable in the laboratory to about 150 angstroms. In the winter of 1920 and 1921 Bowen systematically photographed, in this newly avail- able region, the spectra of most of the first twenty elements of the periodic table. The results were published jointly with Millikan in 1924. Many interesting surprises occurred in this first survey of the new region, such as the discovery that chemically pure aluminum and magnesium electrodes gave

IRA SPRAGUE BOWEN 87 practically identical spectra in the region between 300 ~ ant! 1200 A. At first the investigators even consiclerec! attributing this finding to some transmutation of one element into another by the powerful condensed spark that was used. But more reflection anti investigation showed that these common lines were due to oxygen, always present on the surface of these easily oxidizable metals. The difference in behavior in the new region and in the spectral regions previously ex- plored results from the presence of all the strong lines of these metals in the older, long wavelength range. In 1921 George E. Hale persuaded Millikan to move to the California Institute of Technology as chairman of its executive council and director of the Norman Bridge Labora- tory of Physics, then nearing completion. Arrangements were made for Bowen also to make the move ant] to continue as Millikan's assistant in the new physics group at Caltech. One of the inducements offerer! by Hale was the proximity of the emergent scientific school to the Mount Wilson Observa- tory of the Carnegie Institution of Washington, where the largest telescopes in the world were being used by an active staff in a variety of investigations in astrophysics and cosmol- ogy. More specifically, Hale promiser! Millikan that diffrac- tion gratings would be provided from the new ruling ma- chine that had just gone into operation at the Pasadena head- quarters of the Observatory. During the first year after the move to Caltech, Bowen taught a course in general physics, using a lecture room in Throop Hall because the Norman Bridge L aboratory was still uncler construction. He also participates] with Millikan in research on cosmic rays. The program involved the design and use of instruments carrier! to high altitudes by sounding balloons, the actual flights being made from San Antonio, Texas. The researchers obtained the first record from souncI- ing balloons of cosmic rays and fount! definite evidence for

88 BIOGRAPHICAL MEMOIRS an increase of intensity with altitude. Aerial observations had already been made by Hess and Kolhorster, but because they user! manned balloons they were limiter! to lower altitucles. Bowen also participated with R. M. Otis in measurements of cosmic-ray intensity in the High Sierra of California. They used detectors that were lowered into the waters of mountain lakes at altitucles of some 12,500 feet, such that the water shielded the instruments from local radioactivity of the rocks. A love of the mountains stayed with Bowen all his life, but his principal research interests lay in spectroscopy, to which he soon returned. With the completion of the physics laboratory, apparatus couIct be assembled for the continuation of the ultraviolet studies. An exceptionally fine grating was indeecl provided by I. A. Anderson of the Mount Wilson Observatory. This grat- ing gave much higher resolution than had hitherto been ob- tained in this region anal macle possible the studies of the fine structure of many lines in the extreme ultraviolet that were carried out by Bowen with the vacuum spectrograph in 1923 and 1924. At about this time, Paschen and R. H. Fowler almost simultaneously macle their analyses of highly ionized Al ITI ant] Si IV, anct Bohr publisher! his discussion of penetrating and nonpenetrating orbits. Applying these results to their new data, Bowen ant! Millikan found it possible to make an analysis of B ITI. From further stucties ma(le early in 1924 they were able to show that the so-called regular anti irregu- lar cloublet laws, developed earlier for X-ray spectra, applied equally well to optical spectra when isoelectronic sequences (series of ions of the same electronic structure but differing nuclear charge) were used. This discovery at once ma(le pos- sible a direct correlation between optical and X-ray spectra ant! therefore between the atomic-structure formalisms cle- veloped from these two types of spectra. The results of this

IRA SPRAGUE BOWEN 89 correlation constituted part of the evidence that later resulted in the introduction of the important concept of the spinning electron by UhIenbeck and Goudsmit. The doublet laws provided a very powerful too! for the analysis of highly ionized atoms. In 1925 and 1926 Bowen and Millikan applied these laws to the analysis of their new data and were able to obtain partial analyses of Be I, Be Il. B Il. B IIT, C IlI, C IV, P III, P IV, P V, S IV, S V, S VI, CT V, C l VI, C ~ VIT, C 1 VITI, Y lIl, and Zr IV. In this research, the heavier part of the load fell on Bowen, who produced and measured the spectrograms and analyzed the data. Millikan was exceedingly busy with the administration of the Institute anc! of the Norman Bridge Laboratory, as well as with a variety of other research efforts. He would occasionally cirop in to keep in touch. When Bowen was ready, he would say to Millikan, "I've got an article. How about coming arounct tonight?"* Millikan would appear at about nine o'clock in Bowen's office, and the two would work until midnight writ- ing the paper. For several years after coming to Caltech, Bowen heal the title of instructor and research assistant to the director of the Norman Briclge Laboratory of Physics. His teaching assign- ment was to instruct one of the undergracluate sections of twenty students in physics. In 1924 the practice was initiated of assigning the top men of the sophomore class to section A, the honor section, and Bowen was given this section. Much later he commented that "l never had quite such a run for my money. In the section were Ed McMilIan, Robley Evans, and several others who later became heads of departments or university presidents. Keeping ahead of that group took . quite some time. ~ *Interview with Charles Weiner, Center for the History of Physics, American Institute of Physics. Sibs.

go BIOGRAPHICAL MEMOIRS Bowen continued with undergraduate teaching in physics until 1929, when he took over the teaching of graduate courses in optics and spectroscopy. He became assistant pro- fessor of physics in 1926, associate professor in 192S, and professor in 193 I. Under the pressures of research and teaching, Bowen found little time to proceed with the formal requirements for the Ph.D. degree, although he finally received it in 1926, by which time he had already published some twenty articles. language examinations were required, and partly for this reason he took a month's vacation in the summer of 1925, spending some of the time reading Sommerfeld's Atombau und Spectra1!linien in German. (He had already passed the French examination.) His thesis, somewhat surprisingly, was on the subject of "The Ratio of Heat Losses by Conduction and by Evaporation from Any Water Surface." This came about because Bowen had been assigned to guide the thesis work of another graduate student, an older man who had been with the weather bureau and who proposed to do a thesis on evaporation but later lost interest. Bowen's interest grew to the extent that he worked out a formula for the ratio of heat lost by evaporation and by conduction to the air. showing that this ratio can be determined uniquely from the temperature of the air, the temperature of the water, and the humidity. This quantity, known as the Bowen ratio, is to be found in the literature of meteorology and has been of use in oceanography. His ratio method is now commonly used to measure the evaporation from plant, soil, and water surfaces. As Bowen said later, "When ~ got ready to take my degree, that was the paper that was going to press, so it became my thesis."* His subject was undoubtedly a novel one for the faculty pundits including P. Epstein, R. C. Tolman, and Millikan who sat on his examining committee. * Ibid.

IRA SPRAGUE BOWEN 9 In the middle 1920's the vector model of the atom to account for complex spectra was developed by Russell, Saunders, Pauli, Hund, and others. Bowen applied this theory to the analysis of the more complex spectra of the elements in the first row of the periodic table, using again the data accumulated from the use of the high-resolution spec- trograph. It was thus possible for him in 1926 to fix the low terms of C Il. N III, O IV, N II, O IlI, F IV, O Il. F [II, F II, and F I. This, as it turned out, was preliminary to his most outstanding discovery, the identification of the so-called "nebulium lines" in the spectra of galactic nebulae. These two bright green lines hacI been a puzzle to spectroscopists since their discovery by Huggins some sixty years earlier. In paral- lel with the bright yellow line in the spectrum of the sun's corona, which had been attributed to an unknown element (helium) before the element was discovered on earth, it hacT been conjectured that nebulium was also an unknown but real element. By 1920, however, spectroscopy in the X-ray region had established the sequence of light elements. It was clear that there was no room here for an unknown, while the very strong nebulium lines could hardly be due to a rare element at the heavy encI of the periodic table. Spectros- copists were generally aware of the problem and were alert to any {cads that might provide a solution. H. N. Russell of Princeton was knowledgeable about these matters. In 1927 the text of the classic Astronomy by Russell, Dugan, and Stewart appeared, in which Russell made the suggestion that "The nebular lines may be emitted only in a gas of very low density. This wouIcl happen, for example, if it took a relatively long time for an atom to get into the right state to emit them, and if a collision with another atom in this interval prevented the completion of the process. In such a case, it might require a great thickness of the very rarefied gas to emit these lines strongly enough to be visible" [p. 8381.

92 BIOGRAPHICAL MEMOIRS Bowen bought the two volumes of Astronomy and thus became aware of Russell's summary. Later he related that one evening he came home from the laboratory at about nine o'clock and while preparing for bed was thinking about the energy levels of O I! ant! O ITI anct the "forbicIden transi- tions." According to the theory, there was no way for the atom to get from the D or F states to the S (Iowest or ground) state except through collisions. In a very rare gas, as in a nebula, the rate of collisions was insignificant. What, then, happens to these atoms? Are they stuck forever in the D and F states? Then it occurred to Bowen that, given enough time, perhaps the atoms can, in fact, make the "forbicIden" jumps, although at a low rate. Bowen quickly dressed ant! returned to his office. Since all the data on the energy levels were available in his records, it was easy for him to take the differences and to compute the wavelengths of the forbiciclen lines in a matter of minutes. There they were, correct to a hundredth of an angstrom! "I worked until midnight and had the answer when ~ went home," * he said. The "nebulium" lines were in fact due to forbiciclen transitions between low-lying energy levels of singly and doubly ionized oxygen. The lines were intense because of the immense volume of gas at low pressure in the nebulae. The name "nebulium" couIc! be laid to rest. The solution to the problem was wiclely accIaimecT ant! brought well-deservecl recognition to its author. The initial discovery explainec! half a clozen of the strong- est lines in the spectra of gaseous nebulae, but there were many other fainter lines that required years of work by Bowen anc! others; some were regular permitted lines of hydrogen ant! helium, but many were fainter forbidden lines of various elements. Bowen continued the work for years, * Interview with Charles Weiner.

IRA SPRAGUE BOWEN 93 bent on identifying the elements that might provide an expla- nation of the fainter lines and on solving the larger problem of determining the relative abundance of elements in the gaseous nebulae. Bowen soon became interested! in the possibility of fluo- rescence in nebulae. He noticed that the wavelength of the strong resonance lines of ionized helium (He Il) in the 300-400 ~ region coincided within one- or two-hundredths of an angstrom with certain lines of O Ill. The fascinating possibility occurred to him that ultraviolet radiation from helium, in passing through a rarefied gas containing O Ill, couicI be expected to selectively populate certain energy levels in O ITI; this could give rise to peculiar enhancement of specific emission lines of the latter element. In 1934 Bowen received a letter from W. H. Wright, director of the Lick Observatory, who was one of the chief observers of nebular spectra. New data from the ultraviolet were just becoming available. Wright mentioned that he had new nebular lines in the 3100-3300 ~ region and that the intensities of some were quite abnormal. In response to Wright's inquiry about the strange line intensities, Bowen was able to write back with the explanation. He had lacked the data until that time but hacI the solution in the form of the fluorescence mechanism. It is interesting to note that Wright's new ultraviolet data were made possible by the alu- minum coating recently applied to the mirror of the 36-inch Crossley reflector. The great superiority of aluminum com- pared to silver as a reflective coating for telescope mirrors tract resulted in the development by John Strong in Pasadena of the method for evaporative coating in a high vacuum; this clevelopment, closely relater! to the 200-inch telescope proj- ect, was quickly adopted for all large telescope mirrors. Bowen accepted Wright's invitation to spend the summer term of 1938 at the Lick Observatory as a Morrison Associate.

94 BIOGRAPHICAL MEMOIRS With Arthur B. Wyse, he observed the spectra of gaseous nebulae. This was his first real observational work in astron- omy. The work benefited from new, much faster panchro- matic photographic emulsions that had just become available from the Eastman Research Laboratories, ant] the observers were able to discover numerous new emission lines. For many of these lines, Bowen had the identifications from his labora- tory studies. The spectrograms made by Bowen and Wyse carried intensity calibrations, so that they were able to obtain quantitative results on line intensities. In this way they showed that the composition of the gaseous nebulae, i.e., the relative abundance of the elements, is about the same as that of the sun ant! stars. This statement includes the finding that hydrogen is by far the most abundant element, which Russell had already established for the sun. In later years Bowen carried heavy responsibilities for administration, so he fount! little time for research. Never- theless, he continued some work on the spectra of gaseous nebulae. With the large grating spectrograph at the coucle focus of the 200-inch telescope, he made very significant improvements in the precision of the wavelengths of nebular lines, primarily because the resolution and dispersion of this instrument were far superior to those of the laboratory ancI observatory spectrographs used earlier for the ultraviolet stu- clies from which the term differences were derivecI. He pub- lished this work in 1955, as well as a definitive contribution with L. H. Aller and R. Minkowski on the uniquely rich spectrum (263 lines) of the gaseous nebula NGC 7027. In the course of his observational work, Bowen was im- pressed with the very long exposure times often required to obtain direct photographs or spectrograms of faint objects. It was known that the photographic emulsion, generally de- signed for exposure times of a fraction of a second, does not maintain a reciprocity between light intensity and exposure

IRA SPRAGUE BOWEN 95 time for exposures measured in hours. He originated a pre-exposure procedure of baking plates for a specified time at an elevated temperature, showing that for many emul- sions this would significantly increase the effective speed for long exposures. Astronomers were quick to adopt the baking technique, which often cuts exposure times to 50 percent or less; it has for years been standard procedure at major observatories. The "image slicer" is an optical device originated by Bowen to improve efficiency in recording the spectra of stars or nebulae. Because the image of such an object may be large compared to the width of the spectrograph slit, much light may be lost. The image slicer, consisting of an array of several tiny, carefully shaped mirrors, effectively cuts the image into a series of narrow strips that are optically transposed into a single narrow strip that enters the slit with little loss. THE 200-INCH TELESCOPE PROjECT Mention has already been made of the activity in astron- omy and astrophysics that was so prominent in the scientific life of Pasadena in 192 ~ when Bowen arrived from Chicago. The Carnegie Institution's 60-inch reflector had been in operation on Mount Wilson for thirteen years, the 100-inch Hooker telescope for three years. The researches of Kapteyn and of Shapley had opened new vistas on the structure of our Galaxy. Using the 100-inch, Hubble was soon to clinch the concept of a universe populated by countless galaxies like our own; the evidence for the expanding universe was on the horizon. Meanwhile, stellar spectroscopy was flourishing. This wave of progress was due in large measure to the quality and size of the Mount Wilson telescopes and to the excellent observing conditions provided by the site. While the optical quality of the mirrors was attributable to the skill of G. W. Ritchey, much of the telescopes' success, and in particular

96 BIOGRAPHICAL MEMOIRS their mechanical design, was due to the Mount Wilson en- gineer ant! astronomer Francis G. Pease. It was clear that this sequence of large productive telescopes should not be al- lowed to enc! with the 100-inch. Pease went on to promote the design of a 300-inch telescope, for which in 1921 he pro- clucec! drawings anti a scale model introducing the concept of a large "horseshoe" for the main bearing of the polar axle. In 1928 George E. Hale, at that time honorary director of the Mount Wilson Observatory, successfully launched the project to build a 200-inch telescope and obtained from Rockefeller sources the funcling for this great optical instrument that was destined to be installed on Palomar Mountain. As we shall see, the project was to be completed by Ike Bowen twenty-two years later. The design of the 200-inch telescope was conclucted at Caltech with the close collaboration of astronomers and en- gineers of the Carnegie Institution's Mount Wilson Observa- tory over a period of several years, beginning about 1930. The project was guided by the Observatory Council and by a Policy Committee of which Bowen was a member. His knowl- edge of optics and his aptitude for instrumentation were invaluable here, and, not surprisingly, his responsibilities rapidly increased as the work progressed. Among the impor- tant decisions in which he participated were the choice of the focal ratio of the primary mirror (f/3.3~; the specification of a thin-section, ribbed disk of borosilicate glass; and the a(lop- tion of the Serrurier truss and of the horseshoe mounting with hydrostatic bearings. His influence was also strong in applications of the Schmidt camera, both for use in spectro- graphs and for sky-survey instruments such as the 18-inch and 48-inch wide-angle telescopes at Palomar. Indeecl, the basic parameters of the 48-inch were due to him. Remarkable success was achiever! with this telescope because the aperture, focal length, field size, and correcting-plate material were so

IRA SPRAGUE BOWEN 97 specified that three crucial quantities size of the typical stel- lar "seeing disk," optical aberrations, anti limiting resolution of the emulsion (plate grain)—were equated, each being about 30 microns on the plate. THE WAR YEARS The completion of the 200-inch and 48-inch telescopes was delayed by the entry of the United States into World War Il; this brought to a halt all work on the Palomar Observatory and resulted! in drastic shifts in the activity of all concerned. Bowen accepted responsibility for exterior ballistics on the Caltech ordnance rocket project. This organization, which grew to large size and had an important impact on military operations, was headed by physicist Charles C. Lauritsen, with W. A. Fowler second in command. In close collaboration with military services, it was concerned with all phases of clesign, development, testing, ant! production of solid-fuel rockets for immediate use in the war. Bowen organized the photographic section ant] for nearly four years gui~lecl and participated in the field work and analysis needed to provicle precise data on acceleration, stability, trajectory, blast effects, and other parameters. Thousands of rocket tests were moni- tored from the ground and from the air. On other wartime projects not connected with rockets, Bowen contributed to the development of high explosive (levices by inventing cam- eras capable of cinematography at unprecedented rates. He also colIaboratect in experiments for measuring the transpar- ency of seawater and the penetration of sunlight in the ocean. In August 1945 Vannevar Bush, who headed the wartime Office of Scientific Research ant! Development, travellec3 from Washington to witness the explosion of the first nuclear bomb (the Trinity Test) in New Mexico; he continued on to the West Coast anal, in his other capacity as president of the Carnegie Institution, stopped in Pasadena to tell Bowen that

98 BIOGRAPHICAL MEMOIRS he had been appointed director of the Mount Wilson Observ- atory, to succeed Walter S. Adams on January I, 1946. Thus began another and very different phase of Bowen's career, in which he effectively completed the transition from physi- cist to astronomer, and from researcher to director and . · . aclmlnlstrator. OBSERVATORY ADMINISTRATION For the Carnegie Institution of Washington and the Cali- fornia Institute of Technology, the end of the war brought urgency to the matter of reorganizing and renewing their peacetime effort in astronomy. Bowen was responsible to the two institutions, and in 1948 he was appointed director of the combined Mount Wilson and Palomar Observatories. Most of the staff members were of an older generation. Hale, Pease, and Sinclair Smith had died in 1938. John A. Anderson, executive officer of the 200-inch telescope project, was in poor health and nearing retirement. The unfinished 200- inch mirror was in the optical shop in Pasadena. To Bowen fell the crucial task of guiding to completion the telescope project and of staffing and commissioning the Palomar Ob- servatory. Further, a graduate school of astronomy had to be established at Caltech. It was necessary to plan and guide the main research programs to utilize to best advantage the new facilities that would soon be available, to encourage the appli- cation to astronomy of recent advances in nuclear physics, and to exploit the gains that were being made in technology. To promote cross-fertilization of the two fields—stellar spectroscopy and nuclear physics Bowen initiated a series of informal evening gatherings at his home overlooking lower Eaton Canyon. From time to time the group inclucled such physicists as L. Blitzer, L. Davis, W. A. Fowler, R. B. King, C. C. Lauritsen, T. Lauritsen, H. P. Robertson, S. Rubin, and astronomers W. Baade, H. W. Babcock, P. W.

IRA SPRAGUE BOWEN 99 Merrill, R. Minkowski, R. Sanford, and O. C. Wilson. If one can judge from the later contributions of some of the partici- pants, the discussions that cleveloped at these meetings were highly productive. The main task for the 200-inch telescope was clearly defined: to extend the earlier investigations of the distribu- tion of galaxies in space to the most extreme limits that could be reached and to measure velocities or rectshifts in order to refine and extend the velocity-distance relation. The clevel- opment of more precise methods for the photometry of very faint galaxies was a formidable task, but one that tract to be faced. New and better spectrographs hacI to be provided. The wide-angle, 48-inch Schmidt telescope wouIcT be an es- sential companion instrument for survey purposes and for the study of clusters of galaxies. To Bowen it was clear that research in stellar astronomy was ready to enter a quantitative phase. Much was known about the classification of spectra, and wavelength measure- ments could be made accurately, but the measurement of line intensity (equivalent wicith) was a difficult ant! generally in- exact art. Yet line intensities were the keys to the abundance of the elements in stars, nebulae, ant! interstellar clouds. It was now evident that great advances were to be made in stellar structure, stellar evolution, anti the study of nuclear reactions that produce heavy elements in stars. At many uni- versities and research centers there wouIcI be theoreticians and interpreters eagerly demanding quantitative observa- tional ciata; the instruments at Mount Wilson and at Palomar Mountain must be effectively usecI to help meet this neecI. Bowen himself guided the final stages of polishing and figuring the 200-inch mirror. Such a mirror is extremely sensitive to the functioning of its support system, being sub- ject to flexure that varies as the fourth power of the (diameter and inversely as the square of the thickness. Of necessity,

100 BIOGRAPHICAL MEMOIRS testing of the mirror in the optical shop on the Caltech cam- pus hacI to be done with the mirror on ecige. There was concern that upon being placecl face up in the telescope, the outer rim of the mirror might sag, giving the figure a turned- down edge. To avoid the possibility of having to refigure the whole mirror, it had been decided to leave an optically high zone some eighteen inches in width arounc! the outer edge; after installation in the telescope, the mirror would be tested on stars, and the outer zone polishecI clown to the extent required. This procedure was indeed followed after the mir- ror was placed in the telescope in 1948. The rather lengthy process was one of successive approximations. Bowen, using a Hartmann screen in front of the mirror, photographed the Hartmann patterns of bright stars. He then measured the plates in Pasadena and derived the results in terms of high and low areas of the mirror surface. Then the mirror on its support system was lowered to the floor of the dome where Donald O. Hendrix, the optician, carefully polishecI clown the high areas, using a simple mechanism with small tools. After several iterations that requires! many months, the figure had been brought to a very satisfactory level such that 80 percent of the light of a star was concentrated within a circle 50 microns in diameter. The mirror was then aluminized, ant! the telescope was placed in regular service for observations at the prime focus and Cassegrain focus, beginning in 1950. The successful completion of the 200-inch Hale Telescope was unctoubtectly one of Bowen's major achievements and one in which he inwardly took great and justifiable pride. Observations at the coude focus awaited the construction of a large grating spectrograph. For this, the design was evolved by Bowen from the prototype developed by Adams and T. Dunham, Jr., for the 100-inch Hooker telescope on Mount Wilson. Bowen specified a very long focus (30-foot) collimator, to minimize losses at the slit. The resulting

IRA SPRAGUE BOWEN 101 12-inch beam demanded a larger diffraction grating than could be producer! on a single blank. He was able to devise a method of mounting and adjusting four identical plane gratings that could be used as a composite. For the four interchangeable Schmidt cameras he introduced the "twice through" correcting plate, to be positioned just in front of the gratings. The spectrograph went into operation most success- fully in 1951. When the 48-inch Schmidt telescope was completed in 194S, the test photographs that were made clemonstrated remarkable gains in astronomical photography. On each 14-inch square plate, 6.5 degrees on a sicle, were recordecl vast numbers of stars and galaxies to the faint limiting magni- tucle of 20.3, with exposure times of only 12 minutes in the blue and 48 minutes in the red. (With more modern plates the limiting magnitude is substantially fainter.) Faint filamen- tary features such as supernova remnants, gaseous nebulae, and clusters of galaxies formerly beyonc! reach were now recordable with ease. The Schmidt camera of appropriate size and at a good site hac! outmocled all earlier sky survey Instruments. Bowen at once came uncler strong pressure from certain aggressive staff members to let them put the 48-inch to use for their own researches. He was convinced. however. that the telescope should first be used exclusively to complete a survey of the sky for the general good of astronomy. The region from the north pole to declination -30° couIcI be photographed from Palomar Mountain on about 900 plates. With financial assistance from the National Geographic Society, Bowen organized the Palomar Sky Survey. Each of the 900 fields was to be photographed under good conditions on red and blue plates in immediate succession. Glass copies and paper prints produced under close quality control would be made available at cost to other observatories and research

102 BIOGRAPHICAL MEMOIRS centers throughout the world. The Sky Survey was success- fully carried through between 1949 and 1957 as a result of Bowen's firm administrative control. R. Minkowski super- vised the work and personally approved the plates to be ac- cepted. By 1979, 322 complete sets of prints and twenty glass copies of the Survey had been distributed worldwide. The Palomar Sky Survey effectively enlarged manyfold the volume of the observed universe and formed the basis for several important catalogs and for almost countless research articles. It led to the optical identification of large numbers of radio sources and to catalogs of planetary nebulae, of super- nova remnants, of galaxies, and of clusters of galaxies. Following World War Il the multiplier phototube revolu- tionized astronomical photometry for individual stars. The next step the development of image tubes, wherein the high quantum efficiency and other advantages of the photo- cathode might be applied to the recording and photometry of two-dimensional sky fields was one that held great prom- ise. Commercial television camera tubes were not suited to the low light levels encountered in astronomy, but if a rela- tively simple, reliable image tube could be developed, it would have wide application at many observatories. With the enthusiastic support of Bush, Bowen took the initiative in organizing the Carnegie Image Tube Committee, with Merle Tuve as chairman. The Committee, working with industrial laboratories and observatories over an interval of several years, developed a successful sealed, magnetically focused image tube that was produced in some quantity by the Radio Corporation of America; such tubes were widely adopted for use and remain to this day the instrument of choice in several systems. They provide the astronomer with a convenient image-amplifying device having a quantum efficiency of the order of 20 percent as compared to less than 1 percent for the photographic plate.

IRA SPRAGUE BOWEN 103 The ruling engine mentioned earlier tract been super- secled at Mount Wilson by a newer, more precise machine, and beginning in 1950 this machine began to produce size- able gratings of a quality not available before. Many of these gratings were put to use at Mount Wilson and Palomar; clozens of others, some of large size and very high quality, were sold at cost or given away to various observatories and physical laboratories on a worldwide basis. This distribution was characteristic of Bowen's policy to broaden opportunities for the advancement of science. Not only were gratings given away to scientific groups, but the complete technology of ruling gratings at the Mount Wilson Observatory was freely disclosecl in cletail to three scientific companies interested in commercial production. . A Bowen faced and solvect many challenging problems dur- ~ng his tenure as director of the combiner] Mount Wilson and Palomar Observatories. The basic pattern for the proposed organization had been sketched years before by officers of Caltech anct of the Carnegie Institution, and the plan was understood when Bowen agrees! to take the directorship. It remained for him, in consultation with Caltech President Lee DuBricige anct Carnegie Institution President Bush, to for- malize the agreement for unified operation of the two obser- vatories that was adopted by the trustees of both institutions in 1948. It was not possible for the observatory organization to have a separate corporate existence; ownership of the re- spective facilities was to be maintained by the two sponsoring institutions, and they required separate budgets. The direc- tor wouIcl be equally responsible to the two presidents. Re- search was to be conducted by one integrated scientific staff, together with guest investigators who wouicl be invites! to come from outside institutions. There was emphasis on edu- cation and on opportunities for young astronomers through research fellowships. Such an organization, with dual spon-

104 BIOGRAPHICAL MEMOIRS sorship, is rare, if not unique, in American science. It was no easy task for Bowen, over a period of eighteen years, to maintain a balance between the interests of the two institu- tions, however harmonious they were at the start. Working with the Caltech administration, in 1948 Bowen expanclecl the academic group responsible for instruction in astronomy at Caltech; this group became part of the Division of Physics, Mathematics, and Astronomy, which was admin- istratively separate from the Mount Wilson anti Palomar Ob- servatories. I. L. Greenstein accepted an invitation to come from the University of Chicago to join H. P. Robertson and F. Zwicky, with a clual appointment as professor of astronomy ant! staff member of the Observatories. One of Bowen's principal aims as director of the Mount Wilson and Palomar Observatories was to ensure that the facilities, and especially the 200-inch telescope, would be acl- ministerec! and used at the highest level of efficiency ant! productivity. Practically the entire loact of administration was carried by him personally, with a very minimum of assistance. He called on staff members for advice but only rarely requested that they perform special tasks, and then after careful consideration. Every effort was made to provide each astronomer with maximum time and freedom for research with support for long-term programs. In return, Bowen took it for granted that others wouIc! match his extraordinary capacity for work. Various phases of the rather complex ob- servatory operations were conducted according to policies that he cleveloped ant! applied uniformly. Some inclividuals from outside the organization occasionally found it difficult to unclerstand and to adapt to what may have seemed to them rather rigic! rules. An accomplishment, perhaps insufficiently appreciated, resulted from Bowen's efforts to create observation oppor- tunities for astronomers not connecter] with major observa-

IRA SPRAGUE BOWEN 105 tories. This was particularly important for many in other parts of the United States who lackec! not only large instru- ments but also the good observing conditions that prevailed on parts of the West Coast. The guest investigator program of the Mount Wilson and Palomar Observatories, which Bowen cleveloped and administered with great care, gave substantial opportunities to many, but it fell short of meeting the general needs. This became increasingly evident with the growth of the science cluring the 1950's, and more so after the opening of the space age. The answer was to promote the construction of more large telescopes at good sites by other organizations or agencies. This became one of Bowen's main interests, ant! to this cause he gave generously of his time and energy. Even before 1950, for example, he strongly sup- ported the 120-inch telescope project of the University of California. This support included the transfer of much tech- nical and engineering information; he also lent the services of Hendrix, the optician, to the Lick Observatory to oversee and advise on the figuring of the 120-inch primary mirror. During the formative period of the National Science Foundation and, somewhat later, the creation of the major research facility that became the Kitt Peak National Observa- tory, Bowen's advice was frequently requested by Bush, Robert R. McMath, and many others. In his service on the National Astronomical Observatory Advisory Panel, he wisely insisted! that the several sponsoring universities shouIcT be involved in early decisions as to specifications for the basic instrumental facilities of the new observatory. Bowen's advice was sought by astronomers, telescope en- gineers, ant! instrument designers worldwide who visited Mount Wilson and Palomar Mountain for consultation, to inspect the instruments in detail, and to obtain plans and drawings from the engineering group. Many of the innova- tive features of the 200-inch Hale Telescope are to be founcl

106 BIOGRAPHICAL MEMOIRS in other large telescopes subsequently constructed the list inclucles the 6-meter reflector of the U.S.S.R., the Kitt Peak 84-inch and 150-inch telescopes, the 158-inch telescope of the Cerro Tololo Interamerican Observatory, the 153-inch AngIo-Australian telescope, the 140-inch telescope of the European Southern Observatory, anct others too numerous to mention. Complete engineering drawings of the 48-inch Schmidt telescope at Palomar were given to other observa- tories, so that three or more near-cluplicates are now proc;luc- tive in various parts of the world. Among Bowen's later contributions are authoritative studies of the optical design of large reflectors anct of spectro- graphs. In these articles, he showed that five meters is about the largest single passive primary mirror that can feasibly be constructed] and supported, ant! he emphasized the extreme importance of selecting a site with excellent seeing for any large telescope. He went on to optimize the optical design of three very modern instruments that have been constructed since his retirement as director in 1964. These are the 60- inch reflector at Palomar Mountain ( 1969), the 40-inch Swope telescope (1970), and the 100-inch (2.5-meter) Irenee du Pont telescope of the Carnegie Institution's Las Campanas Observatory in Chile. The performance of this last instru- ment is especially noteworthy, for it yields at the Cassegrain focus a field of critically good definition, 2.1 degrees in cli- ameter, with seeing-limited images over the whole of a single glass plate 50 centimeters on a sicle. Bowen anc! Vaughan accomplishecl this by adding a Gascoigne correcting lens to a Ritchey-Chretien system and by adopting a moderate con- cave bending of the plate. This highly successful clesign climaxed Bowen's contributions to the evolution of the wicle- fielcl, general-purpose telescope. The classic treatment on the design of stellar spectro-

IRA SPRAGUE BOWEN 107 graphs for maximum efficiency is to be found in Bowen's 1962 article (see bibliography). He further improved spec- trographs by devising several ingenious adaptations of the Schmidt camera, using solid or semisolid camera optics. Typi- cally, only two days before his unexpected death, Ike dis- cussed at lunch with several staff members a new spectro- graph that they hoped he could design A Bowen's work was characterized by penetrating physical insight, thoroughness, and integrity; it was generally held that when he provided the answer to a problem, that answer was right. Associates came to appreciate his inner enthusiasm and his satisfaction with solid results, but these qualities never blossomed into exuberance. Ike could be firm in his insis- tence on adhering to principles and procedures that had proved to be correct, but he was a most considerate and unselfish individual who held the deep respect and friend- ship of those who knew him well. 1936. He was elected to the National Academy of Sciences in Ira Bowen and Mary Jane Howard were married in 1929; there were no children. Mary Bowen pursued a career as a child psychologist. With her husband, she provided warm hospitality to numerous gatherings at their home in Alta- dena. Bowen himself read widely in history, especially the history of physics and astronomy, and he was a collector of rare and early editions of scientific books. He also had a substantial collection of ancient coins. Many honors came to Ira Bowen during his lifetime. In the words of Caryl Haskins, "These were the formal tributes to a life of extraordinary service to science and to scientific organization and administration. But perhaps the most permanent of all will be the living inspiration, both profes- sional and personal, that he brought to three generations of

108 BIOGRAPHICAL MEMOIRS colleagues and students and associates, anti their living re- gard and attachment for him and for his wife Mary."* THE AUTHOR HAS HAD the benefit of biographical notes provided by the National Academy of Sciences, of a transcript of interviews from the American Institute of Physics, and of articles written by L. H. Aller, I. L. Greenstein, C. P. Haskins, A. McKellar, O. C. Wilson, and A. H. Vaughan. *Yearbook, American Philosophical Society, 1973: 117.

IRA SPRAGUE BOWEN HONORS AND DISTINCTIONS DEGREES A.B., Oberlin College, 1919 Ph.D., California Institute of Technology, 1926 Sc.D. (honorary), Oberlin College, 1948 Ph.D. (honorary), University of Lund, 1950 Sc.D. (honorary), Princeton University, 1953 PROFESSIONAL APPOINTMENTS Morrison Research Associate, Lick Observatory, 193~ 1939 Director, Mount Wilson Observatory, 1946-1948 Director, Mount Wilson and Palomar Observatories, 194~1964 National Astronomical Observatory Advisory Panel, 1953-1957 PROFESSIONAL AND HONORARY SOCIETIES National Academy of Sciences, 1936 American Academy of Arts and Sciences, 1939 American Philosophical Society, 1940 Royal Astronomical Society, London (Associate), 1946-1973 Astronomical Society of the Pacific, President, 1948 AWARDS 109 Draper Medal, National Academy of Sciences, 1942 Potts Medal, Franklin Institute, 1946 Rumford Premium, American Academy of Arts and Sciences, 1949 Ives Medal, Optical Society of America, 1952 Catherine Wolf Bruce Gold Medal, Astronomical Society of the Pacific, 1957 Distinguished Service Staff Member, Carnegie Institution of Washington, 1964- 1973 Henry Norris Russell Lecturer, American Astronomical Society, 1964 Gold Medalist and George Darwin Lecturer, Royal Astronomical Society, 1966

10 BIOGRAPHICAL MEMOIRS BIBLIOGRAPHY 1921 With Sir Robert Hadfield and S. R. Williams. The magnetic me- chanical analysis of manganese steel. Proc. R. Astron. Soc., 98:297-302. With R. A. Millikan and R. A. Sawyer. The vacuum spark spectra in the extreme ultra-violet of carbon, iron, and nickel. Astro- phys. J., 53: 15~60. 1924 With R. A. Millikan. Extreme ultra-violet spectra. Phys. Rev., 23: 1-34. With R. A. Millikan. The series spectra of the stripped boron atom (B III). Proc. Natl. Acad. Sci. USA, 10:199-203. With R. A. Millikan. The fine structure of the nitrogen, oxygen, and fluorine lines in the extreme ultra-violet. Philos. Mag., 48:25~64. With R. A. Millikan. The assignment of lines and term values in beryllium II and carbon IV. Nature, 114:380. With R. A. Millikan. The extension of the X-ray doublet laws into the field of optics. Phys. Rev., 24:209-22. With R. A. Millikan. Some conspicuous successes of the Bohr atom and a serious difficulty. Phys. Rev., 24:223-28. 1925 With R. A. Millikan. The significance of the discovery of the X-ray laws in the field of optics. Proc. Natl. Acad. Sci. USA,11: 119-22. With R. A. Millikan. A possible reconciliation of Bohr's interpene- tration ideas with Sommerfeld's relativistic treatment of elec- tron orbits. Philos. Mag., 49:923-35. With R. A. Millikan. The series spectra of the stripped atoms of phosphorus (P V), sulphur (S VI), and chlorine (C1 VII). Phys. Rev., 25:295-305. With R. A. Millikan. The series spectra of two-valence-electron and of three-valence-electron systems. Nature, 115:423. With R. A. Millikan. The series spectra of two-valence-electron atoms of phosphorus (P IV), sulphur (S V) and chlorine (C1 VI). Phys. Rev., 25:591-99. With R. A. Millikan. The series spectra of three-valence-electron

IRA SPRAGUE BOWEN atoms of phosphorus (P III), sulphur (S IV) and chlorine (C1 V). Phys. Rev., 25:60() 605. With R. A. Millikan. New light on two-electron jumps. Proc. Natl. Acad. Sci. USA, 11:32~34. With R. A. Millikan. Relations of PP' groups in atoms of the same electronic structure. Phys. Rev., 26:150-64. With R. A. Millikan. Series spectra of the two-valence-electron atoms of boron (B II) and carbon (C III). Phys. Rev.,26:31 () 18. 1926 With R. A. Millikan. Stripped oxygen O VI, the PP' group in O V and new aluminum lines in the extreme ultra-violet. Phys. Rev., 27:14~49. With R. A. Millikan. High frequency rays of cosmic origin I. Sound- ing balloon observations at extreme altitudes. Phys. Rev., 27:353-61. The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev., 27:779-87. Vacuum spectroscopy. I Opt. Soc. Am., 13: 89-93. With R. A. Millikan. Series spectra of beryllium, Be I and Be II. Phys. Rev., 28: 256-58. With S. B. Ingram. Wave-length standards in the extreme ultra- violet spectra of carbon, nitrogen, oxygen, and aluminum. Phys. Rev. 28:444-48. With R. A. Millikan. The ionization potential of O II. Nature, 118:410. With R. A. Millikan. Stripped yttrium (Y III) and zirconium (Zr IV). Phys. Rev., 28:923-26. 1927 The series spectra of boron, carbon, nitrogen, oxygen, and fluo- rine. Phys. Rev., 29:321-47. Series spectra of ionized phosphorus P II. Phys. Rev., 29:51(}12. With R. A. Millikan. Energy relationships and ionization potentials of atoms of the first row of the periodic table in all stages of ionization. Proc. Natl. Acad. Sci. USA, 13:531-34. With R. A. Millikan. Spectral relationships of lines arising from the atoms of the first row of the periodic table. Philos. Mag., 4:561-80. The origin of the nebulium spectrum. Nature, 120:473.

112 BIOGRAPHICAL MEMOIRS The origin of the chief nebular lines. Publ. Astron. Soc. Pac., 39:295-97. 1928 The origin of the nebular lines and the structure of the planetary nebulae. Astrophys. J., 67: 1- 15. The life of atomic states and the intensity of spectral lines. Proc. Natl. Acad. Sci. USA, 14:30-32. Series spectra of chlorine, C1 II, C1 III, C1 IV, C1 V, and of Si II, P III, and S IV. Phys. Rev., 31:34-38. Series spectra of potassium and calcium. Phys. Rev., 31:497-502. Series spectrum of sodium Na II. Phys. Rev., 31:967-68. With D. H. Menzel. Forbidden lines in the flash spectrum. Publ. Astron. Soc. Pac., 40:332~0. 1929 The presence of sulphur in the gaseous nebulae. Nature, 123:450. With H. N. Russell. Is there argon in the corona? Astrophys. I., 69: 19~208. Additional lines in the spectra of C II and N II. Phys. Rev. 34:534-36. 1930 With R. A. Millikan. The significance of recent cosmic ray experi- ments. Proc. Natl. Acad. Sci. USA, 16:421-25. The presence of neutral oxygen in the gaseous nebulae. Phys. Rev., 36:600-601. 1931 Spectrum of doubly ionized carbon C III. Phys. Rev., 38: 128-32. With R. A. Millikan. Similarity between cosmic rays and gamma rays. Nature, 128:582-83. 1932 Spectra of two- and three-valence-electron atoms, Si II, P III, S IV, P IV, and S V. Phys. Rev., 39:~15. Ionization of air by gamma rays as a function of pressure and collecting field. Phys. Rev., 41: 24-31.

IRA SPRAGUE BOWEN 1933 113 With R. A. Millikan. Cosmic-ray intensities in the stratosphere. Phys. Rev., 43:695-700. With R. A. Millikan and H. V. Neher. New high-altitude study of cosmic-ray bands and a new determination of their total energy content. Phys. Rev., 44:24~52. The aberrations of the concave grating at large angles of incidence. J. Opt. Soc. Am., 23:313-15. 1934 The spectrum of fluorine, F II, F III, F IV. Phys. Rev., 45:82-86. The spectrum of chlorine, C1 III, C1 IV, C1 V. Phys. Rev.,45:401-4. The path of a secondary cosmic-ray particle in the earth's magnetic field. Phys. Rev., 45:349-51. The presence of neon in the nebulae. Publ. Astron. Soc. Pac., 46: 145-46. The excitation of the permitted O III nebular lines. Publ. Astron. Soc. Pac., 46: 146-48. The chemical composition of the nebulae. Publ. Astron. Soc. Pac., 46: 186-87. The singlet lines of C1 IV. Phys. Rev., 46:377. With R. A. Millikan and H. V. Neher. Very high altitude survey of the effect of latitude upon cosmic-ray intensities and an attempt at a general interpretation of cosmic-ray phenomena. Phys. Rev.,46:641-52. Also in: Papers and Discussions of the Interna- tional Conference on Physics, London, 1:20~24. Spectra of potassium, K IV and K V, and of calcium, Ca V and Ca VI. Phys. Rev., 46:791-92. 1935 The spectrum and composition of the gaseous nebulae. Astrophys. J., 81:1-16. The low terms in Mn V and Fe VI. Phys. Rev., 47:92~25. The extreme ultra-violet in astronomical sources. In: Zeeman Ver- handlungen, pp. 55-62. The Hague: Martinus Nijhoff. 1936 The galactic nebulae. Scientia, 59:77-86.

114 BIOGRAPHICAL MEMOIRS Forbidden lines. Rev. Mod. Phys., 8:55-81. With R. A. Millikan, S. A. Korff, and H. V. Neher. The latitude effect in cosmic rays at altitudes up to 29,000 feet. Phys. Rev., 50:57~81. 1937 With Everett F. Cox. Ionization of air by gamma-rays as a function of pressure and collecting field II. Phys. Rev., 51:232-34. With R. A. Millikan and H. V. Neher. Measurement of nuclear absorption of electrons by the atmosphere up to 10~° electron volts. Nature, 140:23. With R. A. Millikan and H. V. Neher. The influence of the earth's magnetic field on cosmic-ray intensities up to the top of the atmosphere. Phys. Rev., 52:8(:~88. The low terms in Cr III, Cr IV, Mn IV, and Fe V. Phys. Rev., 52: 1153-56. 1938 With R. A. Millikan and H. V. Neher. New evidence as to the nature of the incoming cosmic rays, their adsorbability in the atmo- sphere, and the secondary character of the penetrating rays found in such abundance at sea level and below. Phys. Rev., 53:217-23. With R. A. Millikan and H. V. Neher. New light on the nature and the origin of the incoming cosmic rays. Phys. Rev., 53: 855-61. The low terms in Co VI. Phys. Rev., 53:88~90. The image-slicer, a device for reducing the loss of light at the slit of a stellar spectrograph. Astrophys. I, 88: 1 13-24. With A. B. Wyse. Hypersensitization and reciprocity failure. Publ. Astron. Soc. Pac., 50:305. With A. B. Wyse. New lines in the spectra of the gaseous nebulae. Publ. Astron. Soc. Pac., 50:34~49. With R. Minkowski. Effect of collisions on the intensities of nebular lines. Nature, 142: 107~80. 1939 With B. Edlen. Forbidden lines of Fe VII in the spectrum of nova RR Pictoris ~ 1925~. Nature, 143:374. With A. B. Wyse. The spectra and chemical composition of the

IRA SPRAGUE BOWEN 1 l; gaseous nebulae NGC 6572, 7027, 7762. Lick Obs. Bull. 19: 1-16. 1940 5 With L. T. Clark. Hypersensitization and reciprocity failure of pho- tographic plates. J. Opt. Soc. Am., 30:50~10. 1946 Metric photography: Field equipment and operations. In: Field Testing of Rockets, pp. 47-89. Pasadena: California Institute of Technology. With F. A. Jenkins. Transparency of ocean water. I. Opt. Soc. Am., 36:617-23. Survey of the year's work at Mount Wilson. Publ. Astron. Soc. Pac., 58:329-40. 1947 With P. Swings. Relative intensities of the coronal and other for- bidden lines. Astrophys. J., 105:92-95. Excitation by line coincidence. Publ. Astron. Soc. Pac., 59: 19~98. Limiting visual magnitude. Publ. Astron. Soc. Pac., 59:25~56. 1948 Survey of the year's work at Mount Wilson. Publ. Astron. Soc. Pac., 60:5-17. The abundance of oxygen in the sun. Rev. Mod. Phys., 20: 10~12. Survey of the year's work at Mount Wilson and Palomar Observa- tories. Publ. Astron. Soc. Pac. 60:353-65. The telescope at work. In: Palomar, fune 3, 1948. San Francisco: Grabhorn Press. Reprinted in: Griffith Obs., 12: 121-23. 1949 The award of the Bruce Medal to Sir Harold Spencer Jones. Publ. Astron. Soc. Pac., 61:61-62. Survey of the year's work at the Mount Wilson and Palomar Obser- vatories. Publ. Astron. Soc. Pac. 61:243-53. 1950 The 200-inch Hale Telescope. Bull. Am. Acad. Arts Sci., 3~4~:2-3.

116 BIOGRAPHICAL MEMOIRS Final adjustments and tests of the Hale Telescope. Publ. Astron. Soc. Pac., 62:91-97. 1951 Survey of the year's work at the Mount Wilson and Palomar Obser- vatories. Publ. Astron. Soc. Pac., 63:~16. Palomar Observatory. Sci. Mon., 73:141-49. With Paul Merrill. The spectrum of RS Ophiuichi in May 1951. Publ. Astron. Soc. Pac., 63:25~56. With Paul Merrill. Forbidden lines in the spectrum of MWC 300. Publ. Astron. Soc. Pac., 63:29~96. 1952 The spectrographic equipment of the 200-inch Hale Telescope. Astrophys. J., 116: 1-7. Optical problems at the Palomar Observatory. I. Opt. Soc. Am., 42: 79~8~)0. Some new tools of the astronomer. Observatory, 72: 12~37. Mount Wilson and Palomar Observatories (Reports of Observa- tories 1951-521. Astron. I., 57:184-85. 1953 Mount Wilson and Palomar Observatories (Reports of Observa- tories 1951-52~. Astron. J., 58:25~61. 1954 The 200-inch Hale Telescope. Trans. Int. Astron. Un., 8:75~54. Mount Wilson and Palomar Observatories (Reports of Observa- tories 195~54~. Astron. I., 59:35~56. Edwin P. Hubble, 188~ 1953. Science, 119:204. 1955 Wavelengths of forbidden nebular lines. Astron. J., 121:30~11. Mount Wilson and Palomar Observatories (Reports of Observa- tories 1954-55) Astron. J., 60:296-99. Astronomical spectrographs: Past, present, and future. In: Vistas in Astronomy, ed. Arthur Beer, vol. l, pp.400-406, London: Perga- mon Press. With L. H. Aller and R. Minkowski. The spectrum of NGC 7027. Astron. I., 122: 62-71.

IRA SPRAGUE BOWEN 1956 117 Optics. Smithson. Contrib. Astrophys., 1: 1-3. Mount Wilson and Palomar Observatories (Reports of Observa- tories 1955-56~. Astron. I., 61: 336-41. 1957 Instrumentation at Mount Wilson and Palomar Observatories. Publ. Astron. Soc. Pac., 69:377-84. 1958 The Universe from Palomar. Griffith Obs., 22:6~78. Astronomy in a changing world. In: Frontiers in Science, ed. E. Hutchings, Jr., pp. 28~94. New York: Basic Books. 1960 John August Anderson, 1876-1959. Publ. Astron. Soc. Pac. 72:9~96. John A. Anderson, astronomer and physicist. Science, 131 :64~50. Wavelengths of forbidden nebular lines II. Astrophys. }.,13?: 1-17. The 200-inch Hale Telescope. In: Stars and Stellar Systems, ed. G. P. Kuiper and B. M. Middlehurst, vol. 1, Telescopes, pp. 1-15. Chi- cago: Univ. of Chicago Press. Schmidt Cameras. In: Stars and Stellar Systems, ed. G. P. Kuiper and B. M. Middlehurst, vol. 1, Telescopes, pp. 43-61. Chicago: Univ. of Chicago Press. 1961 Problems in future telescope design. Publ. Astron. Soc. Pac., 73: 11~24. 1962 John August Anderson. In: Biographical Memoirs, 36:1-18. New York, Columbia Univ. Press for the National Academy of ~ - ~clences. Robert Raynolds McMath (1891-1962~. Yearb. Am. Philos. Soc., pp. 14~53. Spectrographs. In: Stars and Stellar Systems, ed. W. A. Hiltner, vol. 2, Astronomical Techniques, pp.3~62, Chicago: Univ. of Chicago Press.

118 BIOGRAPHICAL MEMOIRS 1963 With L. H. Aller and O. C. Wilson. The spectrum of NGC 7027. Astrophys. J., 138: 101~17. 1964 Explorations with the Hale Telescope. Science, 145:1391-98. Le choix de sites d'observatoires astronomiques (site testing), in- formal discussions. Int. Astron. Un. Symp. no. 19, ed. I. Rosch pp. 15-34. Paris: Gauthier-Villars. Telescopes. Astron . ~ ., 169: 816-25. 1965 With James B. Kaler and Lawrence H. Aller. Spectrophotometric studies of gaseous nebulae. IV. The Orion Nebula. Astrophys. J., 141:912-22. 1966 With Lawrence H. Aller and James B. Kaler. Spectrophotometric studies of gaseous nebulae. VII. The ring planetary NGC 7662. Astrophys. J., 144:291-304. Optimum thermal effects for large domes. In: The Construction o) Large Telescopes, ed. D. L. Crawford, pp. 17() 74. New York: Academic Press. Control of thermal effects. In: The Construction of Large Telescopes, ed. D. L. Crawford, pp. 6~65. New York: Academic Press. Statement of aims and limitations of the program. In: The Construc- tion of Large Telescopes, ed. D. L. Crawford, pp. ~7. New York: Academic Press. With Bruce Rule. The Palomar 60-inch photometric telescope. Sky Telesc., 32: 185-87. 1967 Future tools of the astronomer. (Darwin lecture.) Q. J. R. Astron. Soc., 8:~22. Astronomical optics. In: Annual Review of Astronomy and Astrophysics, ed. Leo Goldberg, David Layzer, and John G. Phillips, vol.5, pp. 4~66. Palo Alto: Annual Reviews.

IRA SPRAGUE BOWEN 119 1968 Comments on accuracy and on optical tests and adjustments of the 200-inch Hale Telescope. In: Symposium on Support and Testing of Large Telescope Mirrors, pp. 8-9; 98-101. Tucson: Kitt Peak Na- tional Observatory and Univ. of Arizona. 1969 With E. W. Denison and M. Schmidt. An image tube spectrograph for the Hale 200-inch Telescope. In: Advances in Electronics and Electron Physics, ed. L. Marton, vol. 28, pp. 767-71. New York: Academic Press. 1972 National Geographic Society-Palomar Sky Atlas. In: National Geo- graphic Society Research Reports, 1955-1960 Projects, ran. 27-32. National Geographic: Wash.. D.C. -at rr <A 1 Astronomical instruments in the twentieth century. In: Legacy of George Ellery Hale, ed. Helen Wright, Joan N. Warnow, and Charles Weiner, pp. 23~49. Cambridge, Mass.: MIT Press. 1973 With Arthur H. Vaughan, fir. The optical design of the 40-inch telescope and of the Irenee DuPont telescope at Las Campanas Observatory, Chile. Appl. Opt., 12:143~34. Milton Lasell Humason. Q. I. R. Astron. Soc., 14:235-37. With Arthur H. Vaughan, fir. "Nonobjective" gratings. Publ. Astron. Soc. Pac., 85:17~76. In Press Telescopes and observational techniques. In: Enciclopedia del Nove- cento, ed. Guiseppe Bedeschi, vol. 6. Rome: Istituto Della En- ciclopedia Italiana.

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Biographic Memoirs: Volume 53 contains the biographies of deceased members of the National Academy of Sciences and bibliographies of their published works. Each biographical essay was written by a member of the Academy familiar with the professional career of the deceased. For historical and bibliographical purposes, these volumes are worth returning to time and again.

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