measured their wavelengths Moseley-style with a calcite-crystal X-ray spectrograph. He found that the X rays scattered by the graphite came out with wavelengths longer than their wavelengths going in: as if a shout bounced off a distant wall came back bizarrely deepened to a lower pitch. If X rays — light — were only a motion of waves, then their wavelengths would not have changed; Compton had in fact demonstrated in 1923 what Einstein had postulated in 1905 in his theory of the photoelectric effect: that light was wave but also simultaneously particle, photon. An X-ray photon had collided elastically with an electron, as billiard balls collide, had bounced off and thereby given up some of its energy. The calcite crystal revealed the energy loss as a longer wavelength of X-ray light. Arnold Sommerfeld hailed the Compton effect — elastic scattering of a photon by an electron — as “probably the most important discovery which could have been made in the current state of physics” because it proved that photons exist, which hardly anyone in 1923 yet believed, and demonstrated clearly the dual nature of light as both particle and wave.
The subtle experimenter lost his subtlety when he shifted from doing science to proselytizing for God. Rigor slipped to Chautauqua logic and he perpetrated such howlers as the notion that Heisenberg's uncertainty principle somehow extends beyond the dimensions of the atom into the human world and confirms free will. Bohr heard Compton's Free Will lecture when he visited the United States in the early 1930s and scoffed. “Bohr spoke highly of Compton as a physicist and a man,” a friend of the Danish laureate remembers, “but he felt that Compton's philosopohy was too primitive: ‘Compton would like to say that for God there is no uncertainty principle. That is nonsense. In physics we do not talk about God but about what we can know. If we are to speak of God we must do so in an entirely different manner.’”
In 1941 war work had already been kind to Arthur Compton's brother, moving Karl to national prominence within the science community and winning an important secret laboratory for MIT. Arthur wanted as much or more. There was the problem of pacifism, his mother's Mennonite creed and a course much discussed at that time in American vestries, a churchly counterpart to isolationism:
In 1940, my forty-eighth year, I began to feel strongly my responsibility as a citizen for taking my proper part in the war that was then about to engulf my country, as it had already engulfed so much of the world. I talked, among others, with my minister in Chicago. He wondered why I was not supporting his appeal to the young people of our church to take a stand as pacifists. I replied in this manner: “As long as I am convinced, as I am, that there are values worth more to me than my own life, I cannot in sincerity argue that it is wrong to run the risk of death or to inflict death if necessary in the defense of those values.”
Arthur Compton was ready, then, “a short time later,” when Bush and the National Academy asked him to serve.
The review committee met immediately with some of Briggs' associates in Washington. A week later, May 5, 1941, it met again in Cambridge to hear from other Uranium Committee members and from Bainbridge. “There followed,” writes Compton, “two weeks spent in discussing the military possibilities of uranium with others who were actively interested.” Compton worked quickly to complete a seven-page report and delivered it to Jewett on May 17.
The report began with the statement that the committee was concerned with “the matter of possible military aspects of atomic fission” and listed three of those possibilities: “production of violently radioactive materials… carried by airplanes to be scattered as bombs over enemy territory,” “a power source on submarines and other ships” and “violently explosive bombs.” Radioactive dust would need a year's preparation after “the first successful production of a chain reaction,” which meant “not earlier than 1943.” A power source would need at least three years after a chain reaction. Bombs required concentrating U235 or possibly making plutonium in a chain reaction, so “atomic bombs can hardly be anticipated before 1945.”
And that was that: no mention of fast-neutron fission, or critical mass, or bomb assembly mechanisms. The bulk of the report discussed “progress toward securing a chain reaction” and considered uranium-graphite, uranium-beryllium and uranium-heavy water systems. The committee proposed giving Fermi all the money he needed for his intermediate experiment and beyond. It also, more originally, discovered and emphasized the decisive long-range challenge of the new field:
It would seem to us unlikely that the use of nuclear fission can become of military importance within less than two years… If, however, the chain reaction can be produced and controlled, it may rapidly become a determining factor in warfare. Looking, therefore, to a struggle which may continue for a decade or more, it is important that we gain the lead in this development. That nation which first produces and controls the process will have an advantage which will grow as its applications multiply.
Bush was in the process of reorganizing government science when he received the NAS report. The NDRC, empowered equally with the military laboratories and the National Advisory Committee for Aeronautics, had served for research but lacked the authority to pursue engineering development. Bush proposed a new umbrella agency with wide authority over all government science in the service of war, the Office of Scientific Research and Development. Its director — Bush — would report personally to Roosevelt. Bush prepared to move up to the OSRD by calhng in Conant to take over the NDRC. “And only after it was clear that I should shortly have a new position,” writes Conant, “did Bush begin to take me into his confidence as he pondered on what to do with the Briggs Committee.” Against the background of his British experience Conant told Bush his reaction to Compton's report was “almost completely negative.”
Jewett had delivered the report to Bush with a cover letter calling it “authoritative and impressive,” but privately he cautioned Bush that he had “a lurking fear” that the report “might be over-enthusiastic in parts and not so well balanced.” Jewett also passed it to several senior colleagues for comment, including the 1923 Nobel laureate in physics, Robert A. Mil-likan of Caltech, and sent their comments along to Bush in early June. Bush responded with exasperation compounded with astonishing confusion about the developments in Britain:
This uranium business is a headache! I have looked over Millikan's comments, and it is quite clear that he wrote them without realizing the present situation. The British have apparently definitely established the possibility of a chain reaction with 238
He agreed that the work “ought to be handled in a somewhat more vigorous form,” but he was still profoundly skeptical of its promise:
Even if the physicists get all that they expect, I believe that there is a very long period of engineering work of the most difficult nature before anything practical can come out of the matter, unless there is an explosive involved, which I very much doubt.
The OSRD director was not yet convinced despite new word of pluto-nium's remarkable fissibility. Segr6 and Seaborg had continued working through the spring of 1941 to determine the man-made element's various cross sections. On Sunday, May 18, having finally prepared a sample thin enough for accurate measurement, they calculated plutonium's cross section for slow-neutron fission at 1.7 times that of U235. When Lawrence heard the news on Monday, says Seaborg, he swung into action:
We told Lawrence about our definitive demonstration yesterday of the slow neutron fissionability of 94239 and he was quite excited. He immediately phoned the University of Chicago to give the news to Arthur H. Compton… Compton made an immediate attempt to phone (unsuccessfully) and then sent a telegram to Vannevar Bush… In his telegram Compton indicated that the demonstration… greatly increases the importance of the fission problem since the available material [i.e., U238 transmuted to plutonium] is thus increased by over 100 times… He said that Alfred Loomis and Ernest Lawrence accordingly have requested him to urge anew the vital importance of pushing the [uranium-graphite] work at Columbia.
