Pauling Becomes a Researcher

Roscoe Dickinson, 1923.

Roscoe Dickinson, 1923.

[Part 2 of 3 in a series investigating Linus Pauling’s life as a graduate student]

As a graduate student at the California Institute of Technology (CIT), Linus Pauling tailored a research program that was focused on the properties of matter, with a particular emphasis placed on molecular structure. This interest and the techniques that he learned would shape Pauling’s scientific thinking for the rest of his life.

Pauling’s focus on the theoretical, and his questioning of why processes move forward as they do or why structures are built as they are, was in keeping with contemporary trends in physical chemistry. Pauling enrolled at Caltech with a strong desire to learn more about the discipline of physical chemistry and his early mentor, Caltech chemistry chair A.A. Noyes, encouraged him to build up his background in x-ray crystallography to further enable this pursuit.

When Pauling began classes in September 1922, he also began his research in x-ray crystallography under the direction of his major professor, Roscoe Gilkey Dickinson.  Not much older than Pauling and a recently minted PhD himself, Dickinson would soon become Pauling’s friend. Within weeks, Pauling began receiving invitations for dinners at the Dickinson house and was soon spending the odd weekend on camping trips with Dickinson and his wife.  After Ava Helen and Linus were married, she too joined in these social gatherings.

Dickinson and Pauling worked closely together for most of Pauling’s first year of grad school, but once Pauling had mastered the techniques necessary to prepare his own research, he mostly moved without Dickinson’s direct supervision. In a 1977 interview, Pauling recalled that Dickinson “was remarkably clear-headed, logical, and thorough” while working in the lab.  And as for the research,

Fortunately the field of x-ray diffraction was in an excellent state in that the procedures were rather complicated but they were thoroughly logical, [and] consisted of a series of logical tests.

The rigor and the logic that were fundamental to the field both pleased Pauling immensely.  And before long, the prodigious young student had moved beyond the expertise of his mentor and had begun to conduct original research that was outside of Dickinson’s own capability. In fact, Pauling’s acumen in the lab and facility as an x-ray crystallographer advanced so rapidly that, by his own recollection

…after about three years…I was making structure determinations of crystals that the technique was not powerful enough to handle, by guessing what the structure was and then testing it.


X-ray apparatus at Linus Pauling's desk, Gates Laboratory, California Institute of Technology. 1925.

X-ray apparatus at Linus Pauling’s desk, Gates Laboratory, California Institute of Technology. 1925.

But in his earlier days, Pauling still needed some help. During November and December of his first year as a graduate student, Pauling prepared approximately twelve crystals and attempted to analyze them using x-rays, but none of the crystals yielded images sufficient enough to make a structure determination.

At this point, Dickinson stepped in and directed Pauling to the mineral molybdenite (MoS2), in the process showing him how to take an adequate sample, mount it, and analyze it using x-ray crystallography. This assistance in hand, Pauling was able to determine the structure of the crystal and Dickinson returned to his own work, confident in his feeling that Pauling was capable of doing the crystallography himself.

Soon after completing the experiment, Pauling was confronted by a very different type of confusion. With a successful structure determination in hand, he assumed that the next step would be to publish the work. So too did he assume that Dickinson would provide him with more direction, but he found that none was offered.  As such, Pauling wrote up his findings and presented them for review to his major professor.

Not long after, A.A. Noyes summoned Pauling to his office and carefully explained to the young graduate student that he had written up a paper with only his name on it and in the process had failed to acknowledge the crucial help that Dickinson had provided. Chagrined, Pauling revised the paper and listed himself as a second author, behind Dickinson. The experience proved to be an important one for Pauling, who was reminded early on of how easy it can be to minimize or discount the role that colleagues can play in one’s own research.


Molybdenite model, side view.

Molybdenite model, side view.

By the end of April 1923, Dickinson and Pauling had submitted their paper on the structure of molybdenite to the Journal of the American Chemical Society (JACS); it was published in June of that same year.  Together they had found the simplest crystal structure of molybdenite – which contains two molecules in a hexagonal unit – based on Laue and spectral photographs, and using the theory of space groups.  Although he published a piece on the manufacture of cement in Oregon while he was in undergrad at Oregon Agricultural College, the molybdenite paper was Pauling’s first true scientific publication.

Later that year, Pauling arrived at another milestone by publishing his first sole-author paper, one in which he described the structure of magnesium stannide (Mg2Sn) as determined, once again, by using x-rays. The paper was a huge accomplishment for another reason as well: the x-ray processes used by Pauling had never been successfully deployed for the study of an intermetallic compound before.  And even though this was his first single author paper, Pauling still made sure to thank Roscoe Dickinson in his conclusion, taking pains to avoid another scholarly faux pas.  He would continue in this practice throughout his graduate career.


Richard Tolman, 1931.

Richard Tolman, 1931.

“The crystal structure of magnesium stannide,” was one of eight articles that Pauling published during his grad school years – he completed an impressive total of six structures before receiving his doctorate. Having authored these articles, Pauling found himself on the forefront of a shift in physical chemistry: as crystallography advanced, it was becoming increasingly clear that the properties of specific compounds were based on their structures, which could now be described with mounting confidence. Indeed, several of Pauling’s articles included reevaluations of existing structures, with revised explanations as to why the structures in question had not complied with the new data that Pauling collected.

One such article was “The Entropy of Supercooled Liquids at the Absolute Zero,” which Pauling wrote with CIT faculty member Richard C. Tolman.  In their paper, the two authors corrected an earlier claim made by Ermon D. Eastman, a professor of physical chemistry at Berkeley, who had stated that complicated crystals (those with large unit cells) have greater entropy at absolute zero than do simple crystals. Using statistical mechanical techniques, Pauling and Tolman were able to show that, at absolute zero, the entropy of all perfect crystals, even those with large unit cells, also has to be zero.


Detail from 'Atombau und Spektrallinien' containing x-ray diffraction images.

Detail from ‘Atombau und Spektrallinien’ containing x-ray diffraction images.

Pauling had become familiar with Tolman through a different means. During his third term at Caltech, Spring of 1923, Pauling took Tolman’s course in advanced thermodynamics, an experience that boosted his subsequent interest in quantum theory. It was also during this period that he read Arnold Sommerfeld’s Atombau und Spektrallinien (Atomic Structure and Spectral Lines) and began to be exposed to cutting edge research in quantum theory through the numerous physics and chemistry research colloquia hosted by Caltech.

Sommerfeld would become a lasting influence on Pauling’s life and Pauling would eventually study with him in Germany while there on a Guggenheim Fellowship in 1926-27. But well before then, in 1923, Sommerfeld visited CIT to talk about his work with the new quantum theory. As an aid to his lectures, Sommerfeld used crystal models that he brought from Germany, which he hoped would help him to better explain this complicated work. Afterward, Pauling felt emboldened enough to to show Sommerfeld some of the models that he himself had made in the course of his own research; models that turned out to be much better than those constructed by Sommerfeld.

Advertisements

Die Chronologie von Linus Pauling

Pauling speaking in Mainz, Germany, July 1983.

Pauling speaking in Mainz, Germany, July 1983.

Since we’re in an announcing mood, it gives us great pleasure to pass along word of another new Pauling resource recently made available online by the Special Collections & Archives Research Center: a German-language edition of Robert Paradowski’s Pauling Chronology.

Robert Paradowski’s chronology of the life and work of Linus Pauling, which we’ve written about in the past, is surely one of the most useful accounts of Pauling’s story available anywhere and almost certainly the best general overview that one can find online.  Paradowski is Pauling’s official biographer.  He knew Pauling well and compiled a significant corpus of one-on-one interviews that surely contain a great deal of unique information.  Those of us who spend time in the Pauling orbit have long anticipated the release of the Paradowski biography, rumored to be a three-volume work, but it has yet to see the light of day.

So until the publication of his epic, Pauling watchers with an interest in Paradowski’s work have to content themselves with the Chronology, which was first published in print in 1991 and later released online by Oregon State University in 2009.  Since then, we have done what we can to increase the accessibility of the text to larger audiences, beginning with a Spanish translation released in 2010.  The new German edition is likewise meant to act in this spirit of increased access to a valuable resource.  Future translations are anticipated as skill sets within the department avail themselves.


Pauling was comfortable with language.  His written English was impeccable – peppered throughout the Pauling Papers, one finds numerous examples of his correcting the grammar or style of other authors – and he was comfortable delivering lectures in essentially all of the romance languages. German, however, was Pauling’s strongest second language.

Carl Pauling, 1915.

Carl Pauling, 1915.

Pauling came from German stock on his father’s side. His grandfather Charles Henry Pauling, whom everyone called Carl, was born in the U.S. to recent German immigrants, and he eventually married a German woman named Adelheit Blanken.  In 1882 Carl and Adelheit moved to Oswego, Oregon, a suburb of Portland, and stayed there for the remainder of their lives.  Linus, who was born in 1901, spent a significant amount of time in his grandparents’ home, especially after his family had settled for good in Portland in 1909.  As Thomas Hager notes in his Pauling biography, Force of Nature, daily life in the grandparents’ home was imbued with the culture of the old country.

…the woodstove was always warm and the smell of rich German cakes filled the air. A sod cellar was packed with home-canned fruits and crocks of sauerkraut and pickles….Carl and Adelheit were devout Lutherans. Because there was no church in Oswego, every month they would invite a minister from across the river to hold services in their house. Linus sometimes sat among the small group of worshipers in the front parlor, listening to the service and hymns sung in German.

This early exposure to German spoken in the home gave Linus a leg up in his later studies of the language, which included two years of undergraduate class work at Oregon Agricultural College and, later, his passing of a compulsory exam during his doctoral studies at Caltech.

This study was of extreme use in that facility with German was crucial for a scientist in the early twentieth century.  Much of the more important work in the physical sciences was being published in German-language journals and many of the leading minds were based at German universities.

An academic procession at the University of Munich, 1927. Note the arrow pointing to Arnold Sommerfeld.  Photo likely taken by Linus Pauling.

An academic procession at the University of Munich, 1927. Note the arrow pointing to Arnold Sommerfeld. Photo likely taken by Linus Pauling.

Pauling gained first hand knowledge of these facts during his crucially important Guggenheim trip in 1926-1927.  Based mostly in Germany, Pauling made contacts with a number of German scientists including Arnold Sommerfeld, an early mentor of great consequence.  Sommerfeld’s lectures made a deep impression on Pauling and it was not long before Pauling was taking notes, writing papers and giving talks in German.  This capacity only sharpened over the course of his European stay and served Pauling exceedingly well for the remainder of his life.

The German translation of Paradowski’s Pauling Chronology is available at http://scarc.library.oregonstate.edu/coll/pauling/diechronologie/page1.html

Pauling and Wilson

[Part 2 of 4]

In 1926, while still in Europe completing his Guggenheim fellowship, Pauling attended history’s first full-term lecture on the new concept of wave mechanics as applied to quantum theory. This course, taught by Arnold Johannes Willhelm Sommerfeld, a renowned German theoretical physicist and a pioneer of quantum mechanics, was historically significant as the first of its kind.  Sommerfeld would later write of the classes,  “My first lectures on this theory were heard by Linus Pauling, who learned as much from them as I did myself.”

Upon returning from Europe to Caltech, Pauling used the knowledge gleaned from his Guggenheim experience to develop his own lecture series on quantum mechanics. Among those who attended these was none other than Albert Einstein who sat in on one of Pauling’s talks in 1930.

The content of this course became the foundation for Pauling’s first textbook, Introduction to Quantum Mechanics with Applications to Chemistry, which he developed with a former Ph. D. student named Edgar Bright Wilson, Jr.

E. B. Wilson, Jr., known to many as Bright, was born in Gallatin, Tennessee in 1908. After graduating from Princeton in 1930, Wilson attended Caltech and, under Pauling’s direction, received his doctorate in 1933. Wilson then became a fellow at Caltech until accepting a position at Harvard in 1934.

E. Bright Wilson, 1970.

In 1935 Wilson and Pauling published their co-authored text, which took the duo over two years to transform from Pauling’s original lecture notes.  The primary goal in writing the volume was to “produce a textbook of practical quantum mechanics for the chemist, the experimental physicist, and the beginning student of theoretical physics,” for the authors firmly believed that quantum mechanics had applications to nearly all scientific disciplines.

Cognizant of the need to guide the less mathematically adept reader “through the usually straightforward but sometimes rather complicated derivations of quantum mechanics,” Pauling and Wilson formatted their content such that it could be understood by those with mathematics training up through calculus, with some limited additional background on complex numbers, differential equations, and partial differentiation.  Pauling and Wilson wrote that

The book is particularly designed for study by men without extensive previous experience with advanced mathematics, such as chemists interested in the subject because of its chemical applications.

In completing the text, the authors acknowledged a number of mentors and colleagues – many of them Caltech contemporaries – for their contributions to both the authors’ own personal knowledge and to the field of quantum mechanics: Arnold Sommerfeld, Edward U. Condon, Howard Percy Robertson, Richard C. Tolman, Philip M. Morse, Leslie E. Sutton, George W. Wheland, Lawrence O. Brockway, Jack Sherman and Sidney Weinbaum. And last, but certainly not least, the authors acknowledged their wives, Emily Buckingham Wilson and Ava Helen Pauling.

In the years following publication, Wilson built a career as a highly successful chemist and an esteemed member of the scientific community. In 1949 Wilson too received a Guggenheim Fellowship, with another to follow in 1970. And in 1975 Wilson was awarded the prestigious National Medal of Science for physical sciences, just one year after Pauling.

Pauling Amidst the Titans of Quantum Mechanics: Europe, 1926

Erwin Schrödinger and Fritz London in Berlin, Germany, 1928.

[Ed. Note: Spring 2010 marks the seventy-fifth anniversary of the publication of Linus Pauling and E. Bright Wilson, Jr.’s landmark textbook, Introduction to Quantum Mechanics.  This is post 1 of 4 detailing the authoring and impact of Pauling and Wilson’s book.]

…the replacement of the old quantum theory by the quantum mechanics is not the overthrow of a dynasty through revolution, but rather the abdication of an old and feeble king in favor of his young and powerful son.

-Linus Pauling, “The Development of the Quantum Mechanics,” February 1929.

Since 1925 the John Simon Guggenheim Memorial Foundation has annually awarded fellowships to promising individuals identified as advanced professionals who have “already demonstrated exceptional capacity for productive scholarship or exceptional creative ability in the arts.”  The selection process is extremely competitive and recipients are generally esteemed in their chosen field as applicants face rigorous screening and are selected based on peer recommendation and expert review.

Since the first awards in 1925, many Nobel and Pulitzer prize winners have received Guggenheim Fellowships including, but not limited to, Ansel Adams, Aaron Copland, Martha Graham, Langston Hughes, Henry Kissinger, Paul Samuelson, Wendy Wasserstein, James Watson and, of course, Linus Pauling.

As one of the program’s earliest honorees, Pauling was awarded his first Guggenheim fellowship in 1926.  Heeding the advice of his mentors, Pauling had applied for the fellowship in hopes of pursuing an opportunity for international study.  Pauling’s advisers had long been insisting that he go to Europe to study alongside the leading experts in the budding field of quantum physics, and the Guggenheim funding provided Pauling with the opportunity to do just that.  It was this fellowship that allowed Pauling to travel abroad in order to learn from the European geniuses of quantum physics and to later become one of the early American pioneers of the new field of quantum mechanics.


Linus and Ava Helen Pauling’s apartment in Munich, Germany. 1927.

The subject of quantum mechanics constitutes the most recent step in the very old search for the general laws governing the motion of matter.

–Linus Pauling and E. Bright Wilson, Introduction to Quantum Mechanics, 1935.

The mid-1920s – the time during which Pauling was awarded the prestigious Guggenheim fellowship – was an exciting period to begin an exploration of quantum theory.  The tides were dramatically shifting in this field of study and the acceptance of the old quantum theory was rapidly declining.

Linus and Ava Helen left for Europe on March 4, 1926, arriving in Europe in the midst of what was a great quantum theory reform.  At the inception of quantum theory, physicists and chemists had attempted to apply the classical laws of physics to atomic particles in an effort to understand the motion of and interactions between nuclei and electrons.  This application was grossly flawed as the classical laws, such as Newton’s laws, were originally generated to represent macroscopic systems.   Theorists soon discovered that the classical laws did not apply to atomic systems, and that the microscopic world does not consistently align with experimental observations.

A series of breakthroughs by prominent theorists in the early- to mid-1920s accelerated the decline of the old quantum theory.  In 1924 Louis de Broglie discovered the wave-particle duality of matter, and in the process introduced the theory of wave mechanics.  Then in 1925, just one year before Pauling began his European adventure, Werner Heisenberg developed his uncertainty principle and thus began applying matrix mechanics to the quantum world.

In 1926, shortly after the Paulings arrived in Europe, Erwin Schrödinger combined de Broglie’s and Heisenberg’s findings, mathematically proving that the two approaches produce equivalent results.  Schrödinger then proceeded to develop an equation, now know as the Schrödinger Equation, that treats the electron as a wave.  (The Schrödinger Equation remains a central component of quantum mechanics today.)  The adoption of wave and matrix mechanics led to the development of a new quantum theory and the overwhelming acceptance of a burgeoning field known as quantum mechanics.


Arnold Sommerfeld and Ava Helen Pauling in Munich, Germany. 1927.

Where the old quantum theory was in disagreement with the experiment, the new mechanics ran hand-in-hand with nature and where the old quantum theory was silent, the new mechanics spoke the truth.

–Linus Pauling, February 1929

Pauling began his work in Munich at Arnold Sommerfeld‘s Institute for Theoretical Physics, a scholarly environment described by biographer Thomas Hager as “a new wave-mechanical universe for Pauling.”  It was this atmosphere that opened the door for Pauling to leave his mark as a pioneer of quantum mechanics.

In the fall of 1926, Pauling began applying the new quantum mechanics to the calculation of light refraction, diamagnetic susceptibility, and the atomic size of large, complex atoms.  Through these types of applications, Pauling developed his valence-bond theory, in the process making significant advancements in the new field of quantum mechanics and expanding our understanding of the chemical bond.

The Martha Chase Effect

Martha Chase and Alfred Hershey, 1953.

Martha Chase and Alfred Hershey, 1953.

The Phenomenon

It pretty well goes without saying that the primary mission of the Oregon State University Libraries Special Collections is to preserve, describe and make available the Ava Helen and Linus Pauling Papers.  Beginning, more or less, with the Pauling centenary in 2001, the main focus of our Pauling-related work has been description and accessibility via the web.  In so doing, we have scanned over one terabyte of data and created, at minimum, tens of thousands of static html pages devoted to the life, work and legacy of Linus Pauling and, to a lesser extent, Ava Helen Pauling.

Knowing this, one might reasonably assume that the top search engine query channeling into the content that we have created would be “Linus Pauling,” or some variant therof.  A reasonable assumption indeed but, as it turns out, quite wrong.  In 2008, as in 2007 and 2006 (a close second in 2005), the top keyword query for those who found our content through search was…”Martha Chase.”

Martha Chase was a geneticist who, in collaboration with Alfred Hershey, made an important contribution to the DNA story as it played out in the early 1950s.  Prior to Chase and Hershey’s work, scientists were mixed on the question as to what, exactly, was the genetic material.  Many researchers, Pauling included, initially felt that the stuff of heredity was contained in proteins.  Others, of course, eventually theorized that DNA was the source of genetic information.  Using an ordinary blender as their primary tool, Hershey and Chase devised a famous experiment which proved conclusively that DNA did, in fact, carry the genetic code.

Diagram of the Hershey-Chase Blender Experiment.  Image by Eric Arnold.

Diagram of the Hershey-Chase Blender Experiment. Image by Eric Arnold.

The breadth of Chase-related content that we have digitized is infinitesimally-small relative to the “reams” devoted to Pauling — this page and this page are pretty much it.  And yet, in the context of search, Martha Chase is the top draw to our resources.  It would seem then, that in the marketplace for information — at least that which is retrieved by search — supply and demand for Martha Chase approach their equilibrium at the two pages devoted to her work on our “Linus Pauling and the Race for DNA” site.

Looking through the web statistics, the phenomenon is remarkably consistent.  Not only has “Martha Chase” been the top search query for our domain over, essentially, the past four years, it was also the top search query for our domain over the final week of 2008.  Indeed, the trend has strengthened to the point where today, those who conduct the simple “Linus Pauling” search in Google will note “martha chase” as a recommended search related to Pauling, though in reality the two had little or no interaction at all.

Learning from the Chase Effect

Looking forward, the Chase Effect has become something that we’re thinking more and more about as we begin to develop new projects for the web.  Our top objective will always be to document Pauling’s impact on any number of fields, but in so doing there likely exists a great deal of opportunity for serving different user groups from what might be called “Chaseian” corners of the web.

To use the old many-fish-in-the-sea analogy, there is a lot of content related to Pauling on the Internet, and though we are the primary contributor to this content, we do compete for pageviews with scads of other extremely diverse projects.  (Take a look at the results for the simple “Linus Pauling” Google search to see how diverse the content providers really are.)  So it’s pretty clear that the Pauling sea is quite large and filled with all manner of creatures.

By comparison, Martha Chase represents a much smaller body of water and, in particular, image searches for her — which is probably where the lion’s share of our successful Chase referrals come from — are dominated by the osulibrary.oregonstate.edu/specialcollections domain.

The idea for future work is to think of the Pauling Papers as a collection of collections in attempting to uncover more Martha Chases.

To an extent we have already, somewhat unwittingly, done this with certain of the Key Participants highlighted on our various documentary history websites.  The Harvey Itano Key Participants page, for example, is the second result returned by Google for “Harvey Itano” searches.  Erwin Chargaff‘s page is seventh,  Arnold Sommerfeld‘s page is eighth and Edward Condon‘s is tenth, to name a few more examples.  In each instance, by developing mini-portals related to specific colleagues important to Pauling’s work, we have created resources that help meet the information demand of a non-Pauling user base.

As we standardize our metadata platforms — upgrading older projects and maintaining the standard for new — and, in the process, increase our capacity to “remix” our digital objects, the idea of enhancing existing mini-portals and creating new ones will emerge as an important consideration for our digitization workflow.  This is something that we’ll be talking a lot more about in the months to come.

The Guggenheim Trip, Part III: Unexpected Colleagues

Walter Heitler, Fritz London, and Ava Helen Pauling in Europe. 1926.

Walter Heitler, Fritz London, and Ava Helen Pauling in Europe. 1926.

The paper of Heitler and London on H2 for the first time seemed to provide a basic understanding, which could be extended to other molecules. Linus Pauling at the California Institute of Technology in Pasadena soon used the valence bond method. . . . As a master salesman and showman, Linus persuaded chemists all over the world to think of typical molecular structures in terms of the valence bond method.” – Robert Mulliken. Life of a Scientist, pp. 60-61. 1989.

After Linus Pauling’s publication of “The Theoretical Prediction of the Physical Properties of Many-Electron Atoms and Ions,” he was ready for an even greater challenge – the problem of the chemical bond was a tantalizing enigma for Pauling, and he wanted more time in Europe to work on it. In the winter of 1926, he applied for an extension of his Guggenheim fellowship and with the help of a particularly complementary cover letter from Arnold Sommerfeld, Pauling was granted six more months of support.

Boosted by this news, he quickly began planning visits to Copenhagen and Zurich, both cities boasting of some of Europe’s finest research facilities. His first stop was Copenhagen, where he hoped to visit Niels Bohr’s institute and discuss ongoing research with the renowned scientist. Unfortunately, he had arrived uninvited and found it almost impossible to obtain a meeting with the physicist. Bohr, with the help of Werner Heisenberg and Erwin Schrödinger, was deeply engaged in research on the fundamentals of quantum mechanics, and was specifically attempting to root out the physical realities of the electron, in the process developing a theory which would eventually be termed the “Copenhagen Interpretation.”

Pauling did, however, did make one valuable discovery in Denmark — that of a young Dutch physicist named Samuel Goudsmit. The two men quickly became friends and began discussing the potential translation of Goudsmit’s doctoral thesis from German to English. Their work did eventually get them noticed by Bohr, who finally granted Pauling and Goudsmit an audience. Unfortunately for the pair, Bohr was neither engaging nor encouraging. Nevertheless, the two continued to work together, their cooperation eventually culminating in a 1930 text, The Structure of Line Spectra, the first book-form publication for either scientist.

In 1926 though, frustrated by his unproductive time in Copenhagen, Pauling departed, stopping briefly at Max Born’s institute in Göttingen before traveling to Zurich where other advances in quantum mechanics promised an interesting stay. Unfortunately, the man Pauling was most interested in, Erwin Schrödinger, proved to be just as unavailable as Bohr. The quantum mechanics revolution was consuming the time and thoughts of Europe’s leading physicists and Pauling, a small-fry American researcher, simply wasn’t important enough to attract the interest of men like Bohr and Schrödinger.

Fritz London

Fritz London

As a result, Pauling chose to converse and work with men of his own status in the scientific community. Fritz London and Walter Heitler, acquaintances of the Paulings, had spent the past several months working on the application of wave mechanics to the study of electron-pair bonding.

Heitler and London’s work was an outgrowth of their interest in the applications and derivations of Heisenberg’s theory of resonance, which suggested that electrons are exchanged between atoms as a result of electronic attraction. Heitler and London determined that this process, under certain conditions, could result in the creation of electron bonds by cancelling out electrostatic repulsion via the energy from electron transfer. Their work on hydrogen bonds likewise agreed with existing theories, including Wolfgang Pauli’s exclusion principle and G.N. Lewis’ shared electron bond. The Heitler-London model was well on its way to contributing to a new truth about the physics of the atom

Walter Heitler

Walter Heitler

Pauling used his time in Zurich to experiment with the Heitler-London work. While he didn’t produce a paper during his stay, the new model made a great impression on him and he returned to Caltech with a renewed sense of purpose. He was preparing to tackle the problem of atomic structure, in all its manifestations, and make history as one of the greatest minds of the twentieth century.

For more information, view our post “Linus Pauling and the Birth of Quantum Mechanics” or visit the website “Linus Pauling and the Nature of the Chemical Bond: A Documentary History.”

The Guggenheim Trip, Part II: The Growth of a Scientist

Linus Pauling, Werner Kuhn, and Wolfgang Pauli traveling by boat in Europe. 1926.

Linus Pauling, Werner Kuhn, and Wolfgang Pauli traveling by boat in Europe. 1926.

My year in Munich was very productive. I not only got a very good grasp of quantum mechanics — by attending Sommerfeld’s lectures on the subject, as well as other lectures by him and other people in the University, and also by my own study of published papers — but in addition I was able to begin attacking many problems dealing with the nature of the chemical bond by applying quantum mechanics to these problems.”
– Linus Pauling. The Chemical Bond: Structure of Dynamics, Ahmed Zewail, ed. 1992.

After his and Ava Helen’s stay in Italy, Linus Pauling was itching to return to the lab. The couple arrived in Munich in the last week of April and the first item on Pauling’s agenda was a meeting with Arnold Sommerfeld.

Sommerfeld, in association with Niels Bohr, was responsible for the Bohr-Sommerfeld model of the atom, a precursor to modern quantum mechanical ideas on atomic structure. At the time of Pauling’s European trip, Sommerfeld was serving as the director of the Institute of Theoretical Physics in Munich. He had spent the past decade building Germany’s community of physicists, nuturing many of Europe’s best scientists on a steady diet of cutting edge research. His lectures, famous by the time Pauling reached Europe, were known for their new and innovative content. As Thomas Hager, a Pauling biographer, explains, “[Sommerfeld] knew everyone in theoretical physics, had collaborated with many of them and corresponded regularly with the rest.” He knew exactly what was happening in his field and made sure his students did too.

Pauling’s first Munich meeting with Sommerfeld was something of a disappointment for the young scientist. Rather than being allowed to continue the work he had begun at Caltech, Sommerfeld chose to assign Pauling mathematical research relating to electron spin – an area that held little interest for him.

After a spell of half-hearted devotion to the electron spin problem, Pauling convinced Sommerfeld to allow him to study the motion of polar molecules. Pauling believed he could clarify portions of the Bohr-Sommerfeld model by introducing the effects of a magnetic field to the existing equations. This caught Sommerfeld’s attention and Pauling was subsequently instructed to continue his research under the stipulation that he provide Sommerfeld with the details of his work for presentation at an upcoming conference in Zurich. Pauling did so, and a few days after Sommerfeld had departed for the conference, he received an order to appear in Zurich to discuss his work.

Once at the conference, Pauling found himself surrounded by the leading physicists of Europe. Wolfgang Pauli, a young German physicist famous for his development of the revolutionary Pauli Exclusion Principle, was among those in attendance. On a whim, Pauling approached his colleague and began explaining his recent work on the Bohr-Sommerfeld model. Pauli was unimpressed. The paradox-riddled Bohr-Sommerfeld model, and Pauling’s work supporting it, was on its way out with the new ideas of quantum mechanics soon to take its place. Pauling’s research was too late to be of any value and Pauli was not shy about telling him so.

After finishing his summer vacationing with Ava Helen in Switzerland, Pauling returned to Munich for the fall semester. It was at this time that Pauling really began to prove himself, developing a reputation for his extensive knowledge and concentrated enthusiasm. Pauling’s most important accomplishment, however, was not his ability to make friends. Instead, it was gaining both the attention and the esteem of Arnold Sommerfeld. Pauling did so by discovering a mathematical error in the work of Gregor Wentzel, a protégé of Sommerfeld. The discovery and correction of this mistake garnered Pauling a great deal of respect in Sommerfeld’s eyes.

As it turned out, Pauling’s discovery of Wentzel’s error resulted in more than just Sommerfeld’s acclaim. It allowed Pauling to apply Wentzel’s work to the calculation of energy levels, which in turn provided the platform for a series of calculations on the energy values for complex atoms. This was a totally new approach to deriving atomic properties and Pauling took full advantage of his discovery, publishing his findings in a paper titled “The Theoretical Prediction of the Physical Properties of many-Electron Atoms and Ions.”

In a matter of months, Pauling had evolved from a star-struck young American to a legitimate player in the European field of quantum mechanics. Fortunately for him, his rise to scientific prominence had only just begun.

Read about Arnold Sommerfeld in “The Duelist” or learn more about this entire story on the website “Linus Pauling and the Nature of the Chemical Bond: A Documentary History.”