The dependence on neutron temperature of the ratio of thermal neutron fission cross sections, , has been measured in heavy water moderator. Satisfactory agreement was obtained with the temperature dependence of the cross sections for Maxwellian neutron spectra calculated by C. H. Westcott from the neutron cross section energy dependence. Measurements have also been made of the spatial distribution of neutron temperature in a tank of heavy water. At the side of the tank facing the graphite thermal column neutron source, an apparent temperature difference between neutron temperature and D2O temperature (initially 44°C) decreased with a relaxation length of about one inch for points inside the tank.