My other introduction to geophysical research was serving as an observer of meteor trails during the Perseid shower of August 1932. Arrangements for the observations were worked out between Poulter and astronomy professor C. C. Wylie of the University of Iowa, using sky "reticles" devised and built by Poulter from welding rods. These six foot long conical devices with an eye-ring at the vertex and a coordinate system of radial and circular rods at the other were mounted on fixed stands. One was located in my back yard in Mount Pleasant and the other in Iowa City, fifty miles to the north. The conical fields of view were positioned so that they included a common volume of the atmosphere spanning the estimated altitude range of meteoric luminosity. During the early morning hours of 22 August, Raymond Crilley manned the Iowa City reticle and I manned the Mount Pleasant one, using accurate watches for coordination. Each of us observed about twenty bright meteor trails. Of these, Wylie identified seven as identical cases. He later published the calculated altitudes of the beginning and end points of each of these trails. At the time, I had the impression that this was the first successful attempt to make such measurements and the impression provided part of the thrill of making them. Later, I learned that my impression was not true. During the ensuing Antarctic expedition Poulter used this system to obtain one of the world's most comprehensive sets of observations of meteor trails. Also he made extensive use of the DTM/CIW magnetometer and the seismograph that I had helped construct. The 1935 graduation ceremony at Iowa Wesleyan College included a public parade honoring Poulter and Admiral Richard E. Byrd. The latter gave the commencement address. I graduated summa cum laude and was the first student to walk across the platform. Poulter moved forward to congratulate me but I was so flustered that I scurried past him, clutching my diploma.
During the summer of 1934, I went by automobile to California with my mother, father, and two brothers to visit prospective graduate schools in the west. Two of my most pleasurable recollections were visits to the laboratories of Jesse Du Mond at Caltech and Paul Kirkpatrick at Stanford. My eyes popped at the elegance and scope of their laboratories and I was deeply grateful for the careful explanations of their research that they gave me, a young kid who had dropped in uninvited. But in the end I followed my family's tradition of attending the University of Iowa. In 1935, the faculty of its Department of Physics numbered five: George W. Stewart, head of the department since 1909, John A. Eldridge, Edward P. T. Tyndall, Claude J. Lapp, and Alexander Ellett. The latest addition occurred in 1928 with Ellett's arrival. My assigned advisor was Tyndall, a warm-hearted and spirited individual with a Ph.D. from Cornell University. My central preoccupation was with introductory graduate level courses based on Slater and Frank's Introduction to Theoretical Physics, Abraham and Becker's Classical Electricity and Magnetism, and Pauling and Wilson's Introduction to Quantum Mechanics; on instructors' original lectures on classical mechanics, statistics, and partial differential equations; and on lectures and laboratories in atomic physics. I found the work rigorous and demanding.
I was eager to start research and soon after my arrival Tyndall introduced me to the art of growing large single crystals of spectroscopically pure zinc and of measuring their physical properties. I completed an M.S. degree in June 1936 with an original experimental thesis, "A Sensitive Apparatus for Determining Young's Modulus at Small Tensional Strains". By that time Ellett, who formerly worked with atomic beams, was actively converting his research interests to the new field of experimental nuclear physics. I decided to join in this work. Together with Robert Huntoon, a more senior graduate student, and others, I helped build a copy of the famous Cockroft-Walton high voltage power supply and accelerator. Our capacitors were made of plates of window glass on which we glued aluminum foil; the rectifiers and the accelerator tube used glass cylinders from a local company which supplied them to service stations for the then prevalent model of gasoline pumps. Everything was improvisation. Central elements of the measuring equipment were an ionization chamber and a Dunning-type pulse amplifier with a voltage gain of about one million, built with vacuum tubes of course, and a nightmare to shield adequately against pick-up of A.C. ripple and coronal discharges, of which we had a plethora. Because of the absence of air conditioning or any effective humidity control, operation during the summer was impossible. But on a good day in the autumn of 1938, we finally got an ion beam of a few microamperes with an accelerating potential of 400 kilovolts. My objective was to measure the absolute cross section of the reaction
H2 + H2 -> H1 + H3over as great a range of bombarding energy as possible. The novel feature of my experiment was the use of a gaseous (i.e., infinitesimally thin) target which involved the controlled flow of deuterium gas through the custom-built reaction chamber. After several months of fixing leaks in the vacuum system, replacing burned out filaments in the rectifiers, repairing damage from high voltage spark-overs, etc., etc., I finally got everything to work at the same time. With the help of a fellow graduate student, I then made a continuous run of 40 hours, being unwilling to turn off anything because of the well-founded expectation that many weeks might be required to restore full operation. However, with good luck, I was able to make a confirmatory run two weeks later. These two runs provided the basis of my Ph.D. dissertation which, with Ellett's approval, I then wrote up under the title "Absolute Cross-Section for the Nuclear Disintegration H2 + H2 -> H1 + H3 and Its Dependence on Bombarding Energy" [50 to 380 keV]. I defended my work successfully before the examining committee and received the degree in June 1939.
Following an oral paper that I gave at the spring 1939 American Physical Society meeting, Hans Bethe expressed a keen interest in the results but found that the trend of my curve of cross section vs. bombarding energy was impossible to believe at the lower energies because of basic quantum mechanical theory. This criticism was unsettling to put it mildly. Ellett and I went over the entire matter critically and eventually realized that my method of measuring the beam current through the reaction chamber was faulty. I had collected the ion beam in a Faraday cup after it had passed through the chamber and had measured the charge collected per unit time there. I failed to take account of the partial neutralization of the beam by charge exchange in the target gas, an effect of increasing importance at the lower energies. As a result, the measured current was too low and the calculated cross section was correspondingly too large. A follow-on experiment by Stanley Atkinson, using the same apparatus, established the magnitude of this effect and corrected my results.
Many years later, the cross section of the deuteron-deuteron reaction at much lower energies became a matter of importance in the development of equipment for the current major effort on achieving controlled fusion in the laboratory.