Meanwhile, physicists were developing a whole range of atomic theories to explain the physical properties of bodies in terms of very simple atoms or particles. During the last thirty years of the century the position changed, as physicists and chemists came to agree on a common atomic theory. But the last prominent opponents of atomism were not converted until the early years of the twentieth century, by which time studies of radioactivity had made it clear that the billiard-ball Daltonian atom must, in any case, be abandoned.