By ROBERT DEAN CLARK
     Assistant Editor

     For a generation following World War II, a name as well known in exploration as any other was Lewis Nettleton, an unlikely pretender to such eminence. At that time many industry pioneers still reigned, some who were builders of corporate empires, naturals for celebrity. Nettleton was their antithesis, by comparison almost invisible. He was low key and scholarly, working mostly in the scientific purity of the laboratory, well away from the rough-and-tumble of the field. He became renowned and his influence widespread for a reason divorced from his professional accomplishments: he wrote the book.
     Nettleton's Geophysical Prospecting for Oil, published in 1940, remained a standard introduction to the field for many embryonic explorationists for 30 years before advancing technology finally forced it out of print. It was also widely used by a group not expected to be among its audience - practicing exploration geophysicists.

     Two other books, Geophysical Exploration by C. A. Heiland, and Exploration Geophysics by J. J. Jakosky, appeared almost simultaneously with Nettleton's. Both looked more scientifically formidable and likely to corner professional interest. Heiland's ran to an encyclopedic 1,013 pages, Jakosky's 786. Nettleton's was a skinny 444 and candidly stated, in the second paragraph of the preface, that its intended audience was "the student or lay reader rather than the geophysical specialist." Ironically, its comparatively modest dimensions and scope and an unforbidding writing style became its greatest attractions for working explorationists. Some began calling it their Bible.
     "It was just so damn readable and practical," says Nelson Steenland, a graduate student when it was published and later one of Nettleton's closest colleagues. "The other books were three times as long, full of specialized knowledge and long on detail that nobody was going to use. Nettleton's was a book the practicing geophysicist could just pick up and learn quickly from. There was a lot of accent on fast methods of interpretation. People could grasp the meaning of a gravity anomaly and relate it to structure without living in a dream world."

     In the final pages of his book, Nettleton departed from its strictly instructional tone to make a diplomatic overture toward ending the less than intimate, often hostile relationship then prevailing between geophysicists and geologists. Nettleton's attitude was not countenanced by some oil companies which felt interaction would contaminate rather than enhance the separate interpretations. They made it standard practice to keep geophysicists and geologists apart. Thus, Nettleton challenged a professionally endorsed body of opinion when he wrote:

      Up to the present time geophysical interpreters are either physicists who have learned some geology or geologists who have learned some physics. The two sciences do not mix easily, for the physicist trained in an exact science, controlled by experiment and by well-established laws, may stand aghast at the geologist, who, figuratively, pushes on a pad of paper until it buckles in the middle and seems to consider the experiment a justification for a theory on the mechanics of the formation of the Appalachian Mountain system. On the other hand, many a physicist whom geophysics has brought into contact and cooperation with good geologists has gained a great deal of respect for the breadth of vision that brings order into a tumbled mass of mountain scenery; builds up a complex history of advancing and receding seas over millions of years of time from observations of fossil bugs, size of sand grains, and the chemical nature of very dull-looking and superficially nondescript chunks of rock; or guesses that an im
     portant geological disturbance lies beneath an area because of some very nebulous and apparently unimportant and insignificant variation in the surface material.
     The differences in background have led to some conflict between geologists and geophysicists and not a little blaming of one another for faults of commission and omission.
     There has been some debate in geological and geophysical journals on the question of geophysical interpretation in terms of a geologically "acceptable" or perhaps more properly "natural" underground picture. The geologist has felt that the geophysicist is presumptuous, and the geophysicist has felt that the geologist is too conservative in recognizing departure from recognized type geologic situations u It is the variation in judgment and weighing of the several geophysical and geological elements involved - which in the final analysis is a matter of probability - that has led to accusations and a certain amount of antagonism between geologists and geophysicists.
     Better geophysical maps will be made by geophysicists, and better use of them by geologists will come about, when the two sciences attain more complete coordination. We may even hope for the day when a really competent combination of geologist and physicist will emerge in the same man who will truly be a "geo-physicist" in all that combined title implies.
     
     Nettleton's "geo-physicist" was an ideal, not expected until some time after the two disciplines had at least managed détente, if not become wholly fused. But a few people already deserved the title and all that it implied; Nettleton's own claim was strong. His formal education had been in physics, climaxing in 1923 with a doctorate from the University of Wisconsin. He mastered geology later, without any classroom work. Only six years after initiating his self-education in the "alien" field, he published a theory of great influence. It was an amazing scientific achievement. Prior to entering petroleum exploration at age 32, Nettleton's only contact with geology had been tangential - the enjoyment of the natural beauty of his native Idaho.

     He was born in the small town of Nampa in 1896 and lived in the state until graduating from the University of Idaho in 1918. Although he has spent most of his long life far removed from this area, he has always considered himself a westerner, and his library - drastically purged a few years ago when he moved into an apartment too small to hold the bulk of his collection - retains many books about his home state.
     Nettleton did all his graduate work at Wisconsin. There he met and married Marion Moore. The marriage, called "a priceless relationship" by Nettleton's former partner Tom LaFehr, endured more than 50 years until Marion's death. Nettleton always remembered his anniversary in that half-century; Marion cleverly set their wedding on his birthday. She was a journalism graduate and he gives her expert copy reading some credit for the development of the writing style which played a major role in his career.

     After receiving his doctorate, Nettleton joined the Union Switch and Signal Co. and moved to Pittsburgh. Five years later he became a geophysicist when Gulf, also headquartered in Pittsburgh, started one of the petroleum industry's initial research departments. Nettleton was among the first hired, one of many inspired staffing decisions. Within a year of its founding, the department's directors had put four men on salary - Nettleton, E. A. Eckhardt, Sigmund Hammer, and R. D. Wyckoff - later elected president of the Society of Exploration Geophysicists. They and two scientists already with Gulf, L. P. Garrett and Paul Weaver (SEG's second president), would be the Society's 4th, 7th, 10th, 11th, 20th, and 23rd Honorary Members.
     In the early 1930s, they were joined by John Bardeen who worked with Nettleton, Hammer and others on methods of correcting and interpreting gravity and magnetic data. Bardeen left exploration after two years, returning to Princeton to complete his doctorate. He was awarded the Nobel Prize in 1956 (as a co-inventor of the transistor) and in 1972 (for the theory of superconductivity), becoming the first two-time physics laureate.

     Nettleton's first assignments at Gulf were interpretation of torsion balance data. In 1924 the balance had found the Nash salt dome in Texas, the first oil field discovered by geophysical exploration. Four years later, when Nettleton joined Gulf, it was still the only reliable method of gravity measurement and thus among the geophysicist's key tools since seismic profiling had not been perfected.
     "The torsion balance gave accurate data but it was a very cumbersome, painfully slow process," Nettleton says. "The instrument was about six feet high and awkward to operate. You could only make about three stations a day. Usually two were used together so you got six a day."

     Hammer, who joined Gulf four months after Nettleton and worked with him for nearly two decades, recalls: "Torsion balance data came to us in various forms - raw field data or maps and reports. From this information the horizontal gradient of gravity and the so-called differential curvature were calculated. Originally the geological interpretation of torsion balance data was made directly from the gradient and curvature data. The map of the Nash dome was interpreted that way. The first project Nettleton and I did together avoided this cumbersome process. We integrated the gradients with a special chart to produce a gravity anomaly contour map. That was much easier to interpret."
     Early in the 1930s, pendulums were developed for gravity data collection but the process remained tortuous until the middle of that decade when the first reliable gravimeters arrived. Nettleton comments: "Those early ones could make a measurement in maybe five minutes and they kept getting smaller and faster. They could make 30-40 stations a day and completely replaced the torsion balance and pendulum. If you needed really rapid work, they could make as many as a hundred stations a day."

     Gulf scientists had major roles in the development of both the pendulum and gravimeter, but Nettleton played little, if any, part in either. His specialty was interpretation. In the 1930s, Gulf was considered the industry leader in gravity work and Nettleton was soon one of its stars. His reputation grew steadily and he became chief of Gulf's gravity section.
     Simultaneously, Nettleton was establishing himself in academic circles as a geologist. Steenland says, "He knocked himself out to learn geology. He went on every conceivable field trip and joined all the societies." In Nettleton's 1956 citation for SEG Honorary Membership, Steenland wrote:

     Perhaps his most unusual achievement is this mastery of geology. Without having had any formal training in geology, he has served the Geological Society of America for three years as a member of its projects committee which screens the applications for funds for research projects. In addition he has been one of four civilian members on the panel on geology of the committee on geophysical sciences of the Defense Department's Research and Development Board. These facts illustrate his never-ending effort to correlate geophysics and geology - to use geophysics as a geologic tool.
     
     Nettleton's mastery of geology came quickly. In 1934 he published Fluid Mechanics of Salt Domes, soon recognized as an important hypothesis on salt-dome genesis. Nine years later another important paper described model experiments of the theory. The late Milton Dobrin, himself an extraordinary influence in exploration and still another Nettleton associate to serve as SEG president, earned a Master's Degree by quantitative analysis of Nettleton's model.
     During the '30s, Nettleton also thrust himself in a third direction - teaching - which would also have great impact. Gulf's research department grew swiftly in its early years. By 1930 the geophysical staff in Pittsburgh exceeded 100 and it continued to grow throughout the decade despite the depression. Geology graduates of the University of Pittsburgh seemed an obvious talent source. But Hammer says:
     "They were completely unqualified. We wanted to hire them but they couldn't do the quantitative work. Geology was then a purely descriptive science. Physics was emphasized in our early work. Every project challenged our skills as physicists to come up with new procedures, new formulae, quantitative concepts. Trained geologists did not possess those qualifications at that time."

     Nettleton convinced Gulf to let him teach geophysics, a half day each week, to Pittsburgh geology students. He himself was still new to the field when he began this class and he started "by staying one step ahead of the students." The course became more refined during the decade and Nettleton's lecture notes more detailed, ultimately evolving into the primary source material for Geophysical Prospecting for Oil.
      The book established Nettleton as one of the profession's most capable writers, a craft he had been mastering since the early '30s and which he would vigorously pursue for several decades. He published nearly 50 articles in scientific journals. He confesses his reasons for such a large output were not always purely scientific.
     "Gulf was quite generous about writing papers but wasn't very generous about going to meetings. So I had a motive. It didn't take me long to write a paper so I would think one up and get it on the program. I got to go to a lot of meetings that way."
     Nettleton's writing was a factor in the evolution of SEG's journal Geophysics to its esteemed status in the scientific community. Because of the strict secrecy pervading exploration in the 1930s, high quality papers were rarely available for publication. Nettleton joined the Society in 1936, the same year Geophysics was launched, and quickly became a prolific contributor. He had six articles in the first 10 volumes, a significant percentage since the journal was then a quarterly. Of great influence was 1942's Gravity and Magnetic Calculations. It contained a method of handling solid angles that, a generation later, provided the basis for the first practical computer algorithm for conversion.
     An article of interest in and out of the geophysical community discussed Gulf's role in assuring a secure supply of chromium during World War II. The primary US supply from Turkey had been cut off. Nettleton and Hammer supervised a detailed study of chromite ore in Cuba which substantially added to US reserves.

     Nettleton's writing skills led directly to his one major career move, the 1946 departure from Gulf to become a partner in Torsion Balance Exploration in Houston. Steenland flatly claims that Nettleton's articles were the overriding reason he was offered a partnership after one of the firm's three founders left the company. He says, "The two remaining partners simply began reading geophysical literature to find a candidate for their new technical partner. The search ended with Dr. Nettleton. They found this guy could write stuff they could understand. That's why they hired him away from Gulf. He was hired strictly on the basis of his writing. It was always clean and unpretentious, kind of like the man."
     Nettleton's book and articles had by then made him known and respected throughout the profession. In 1945, just before he joined the great exodus of explorationists to Houston, he was elected SEG editor. Following that two-year term, he was elected vice-president and president, becoming one of very few to serve four consecutive years on the executive committee. In that span, he also served as special editor of two important Society projects, Early Geophysical Papers (1947) and Geophysical Case Histories, Volume I (1948).
     The latter was a particularly delicate undertaking since case histories, then and now, are among the most sensitive items in exploration. The Society formed a 27-member Geophysical Case Histories Committee which was a glittering assembly of industry notables. It included Everette DeGolyer, J. C. Karcher, Henry Salvatori, Gerald Westby and representatives from the major oil companies.

     The shift to Houston radically changed Nettleton's professional life. For the first time, he began to travel regularly to the field, particularly overseas, to taste at first hand the fiercely competitive side of the industry and to experience wild variations in business activity. But he adjusted without altering his polished, low-key style.
     Shortly after he signed on, the company changed its antiquated name to Gravity Meter Exploration and began pioneering in an area few thought commercially feasible - offshore gravity. Under Nettleton's supervision, GMX developed reliable methods for offshore work. It became such an important part of the firm's overall business that it entered into an informal agreement with noted instrument manufacturers LaCoste and Romberg by which GMX had first option on all new meters. GMX acquired the first 12 underwater gravimeters built by LaCoste and Romberg and in the 1960s, when shipboard gravity became operational, bought the first shipboard instruments built by that firm.

     Steenland, who became a GMX partner in the early 1950s, worked intimately with Nettleton on these projects. He remembers the experience as unfailingly pleasurable and intellectually exciting.
     "I first got to know him in the early '40s when I was a graduate student under George Woollard. Nettleton kept hounding George about the work we were doing in the Appalachian Mountains. That raised my eyebrows. Here was this so-called commercial fellow who was really interested in structure.
     "Later I was looking around for a small company to work for and I saw that Nettleton was now with GMX. That impressed me and I thought it would be a good place for me. It was a real privilege to launch my career under such grace and tolerance. There was never a nasty moment. He was always thoroughly decent and probably the world's most lovable guy. His work was characterized by a completely rational mind and a very large absence of prejudice. He was always wanting new information and evaluating it non-hysterically. He wasn't really highly creative, not a wildly imaginative chair-throwing genius. His brilliance depended on consistency and patience. He was always logical, almost mistake-proof. He remained a benign person who was always looking for something new and who just thrived on new ideas."

     By the 1960s, Nettleton had become a regal figure to young gravity practitioners like Tom LaFehr who became one of his partners in 1964. LaFehr is the current SEG president, extending the string of men elected to that office with whom Nettleton has had close professional ties.
     "Working with Dr. Nettleton was an extraordinary experience and being able to be with him and his wife on many social occasions was an honor," LaFehr says. "He has the unusual gift of being able to combine the practical side with difficult material. His real forte was to explain things so the average guy could understand. He could put things into down-to-earth terminology.
     "It's hard to praise him too highly. He is a real gentleman. I don't remember a time when he ever let an argument itself become a driving force. By the time I got to know him, he was a walking encyclopedia; I wondered if I should take up his time. But he never gave me that impression. He was always accessible. He never showed any condescension. He was always willing to sit down and talk on an equal basis and I think he made everyone feel that way."

     GMX went through several management and ownership permutations, starting in the late 1950s, as gravity's share of exploration steadily waned. Nettleton remained a vigorous pro-gravity partisan (he coined the famous phrase "the other 5%") but his campaigning was largely ineffective. GMX faded completely out of exploration in 1978.
     Nettleton, despite his company's decline, maintained an unflagging work rate. He revised his book (Gravity and Magnetics in Oil Prospecting appeared in 1976 when he turned 80), did consulting work, and taught at Rice University. He generally spent about five hours a day in his office until serious health problems finally mandated retirement after more than 50 years in exploration.

     His career, even Nettleton's admirers admit, was not filled with high drama. The much honored King Huberg [TLE, February 1983], who served with Nettleton on SEG's Executive Committee, says, "He was a calm, careful, responsible, scholarly person who turned out consistently high quality, important scientific work."