In June 1972, Robert C. Richardson, an experimental physicist at Cornell University, was visiting England and passing through the University of Sussex, where Dr. Leggett was a professor, when he asked to speak with him. Dr. Richardson wanted to discuss some puzzling results that he and two of his Cornell colleagues, David M. Lee and Douglas Osheroff, had obtained from experiments on freezing helium-3, a rare type of helium that is very difficult to work with at low temperatures. Its far more common cousin, helium-4, is the gas often used to make balloons float.