On a static criterion for the stability of the equilibrium

In a previous paper the stability of the equilibrium of an isentropic spherically symmetric relativistic star has been related to the existence inside the configuration of the zeros of a functionu. This function, which is a solution of a differential equation, appears there as a pure mathematical tool. Nevertheless it is susceptible of a physical interpretation which is drawn out in the present work. This interpretation allows an inquiry into the relation between the above static condition and the well-known dynamic criterion stated by Chandrasekhar and by Misner and Zapolsky on the stability of the equilibrium.Work done in the Laboratorio Astrofisico di Frascati, Roma, Italy.