frequency of seismic events). Tsarapkin responded positively to the US proposal, though was wary of the prospect of allowing underground tests registering below magnitude 4.75. In its own proposal offered 19 March 1960 the Soviet Union accepted most US provisions, with certain amendments. First, the Soviet Union asked that underground tests under magnitude 4.75 be banned for a period of four-to-five years, subject to extension. Second, it sought to prohibit all outer-space tests, whether within detection range or not. Finally, the Soviet Union insisted that the inspection quota be determined on a political basis, not a scientific one. The Soviet offer faced a mixed reception. In the US, Senator Hubert Humphrey and the Federation of American Scientists (which was typically seen as supportive of a test ban) saw it as a clear step towards an agreement. Conversely, AEC chairman John A. McCone and Senator Clinton Presba Anderson, chair of the Joint Committee on Atomic Energy, argued that the Soviet system would be unable to prevent secret tests. That year, the AEC published a report arguing that the continuing testing moratorium risked "free world supremacy in nuclear weapons," and that renewed testing was critical for further weapons development. The joint committee also held hearings in April which cast doubt on the technical feasibility and cost of the proposed verification measures. Additionally, Teller continued to warn of the dangerous consequences of a test ban and the Department of Defense (including Neil H. McElroy and Donald A. Quarles, until recently its top two officials) pushed to continue testing and expand missile stockpiles. Shortly after the Soviet proposal, Macmillan met with Eisenhower at Camp David to devise a response. The Anglo-American counterproposal agreed to ban small underground tests (those under magnitude 4.75) on a temporary basis (a duration of roughly 1 year, versus the Soviet proposal of 4–5 years), but this could only happen after verifiable tests had been banned and a seismic research group (the Seismic Research Program Advisory Group) convened. The Soviet Union responded positively to the counterproposal and the research group convened on 11 May 1960. The Soviet Union also offered to keep an underground ban out of the treaty under negotiation. In May 1960, there were high hopes that an agreement would be reached at an upcoming summit of Eisenhower, Khrushchev, Macmillan, and Charles de Gaulle of France in Paris. A test ban seemed particularly close in 1960, with Britain