Part 1. The neutron fission cross section of U237 has been measured in a thermal neutron spectrum and in a somewhat degraded fission spectrum. The fission cross section for thermal neutrons is found to be <2 barns; the ratio of the fission cross section of U237 to that of U235 in the degraded fission spectrum is found to be 0.476 +- 15% which corresponds to [formula] in this spectrum equal to 0.66 +- 0.10 barns. Part 2. The average neutron fission cross section of U237 has been measured in a neutron energy range extending from approximately 100 ev to fission spectrum. the average fission cross section in this spectrum is found to be 0.70 +- 0.07 barns. Part 3. The low thermal fission cross section for U237 (<2 barns) indicated that the excitation function for fission probably shows an effective threshold. If the excitation function is like all other heavy element (Z > 90) neutron fission excitation functions, it will exhibit a region of approximate constancy starting at a neutron energy of 0.5 to 1 Mev above its effective threshold and extending to a neutron energy in the neighborhood of 5.5 Mev. A hypothetical excitation function for neutron fission of …