Oppenheimer worked very hard [in the spring of 1929] but had a gift of concealing his assiduous application with an air of easy nonchalance. Actually, he was engaged in a very difficult calculation of the opacity of surfaces of stars to their internal radiation, an important constant in the theoretical construction of stellar models. He spoke little of these problems and seemed to be much more interested in literature, especially the Hindu classics and the more esoteric Western writers. Pauli once remarked to me that Oppenheimer seemed to treat physics as an avocation and psychoanalysis as a vocation.