In this article, we develop the calculation of the potential generated by a homogeneous wire bent into a circular shape [1]. In a second time we develop a new method of perturbation. It gives an expression of the potential in terms of R, the radius of the circle. The potential is expressed as a sum of the Newtonian and a small term. The former will be considered as a perturbation. We give the orbits of a test particle in accordance with the initial conditions. Precession of perihelia or chaotic cases is proved [2]. In an accurate way, we must use a juxtaposition of such circular wires, in order to built a two dimensional disc.