In recent years, a new field of nuclear research has been opened through the possibility of studying nuclei wih very large values of angular momentum, temperature, pressure and number of particles. This development has been closely associated with heavy ion reactions, since collisions between two heavy nuclei are especially effective in producing metastable compound systems with large angular momentum, and in transferring energy which is distributed over the whole nuclear volume. Under the strain of temperature and of the Coriolis and centrifugal forces, the nucleus displays structural...