  We describe the effects of phase coherence on transport and thermodynamic
properties of a disordered conducting network. In analogy with
weak-localization correction, we calculate the phase coherence contribution to
the magnetic response of mesoscopic metallic isolated networks. It is related
to the return probability for a diffusive particle on the corresponding
network. By solving the diffusion equation on various types of networks,
including a ring with arms, an infinite square network or a chain of connected
rings, we deduce the magnetic response. As it is the case for transport
properties --weak-localization corrections or universal conductance
fluctuations-- the magnetic response can be written in term of a single
function S called spectral function which is related to the spatial average of
the return probability on the network. We have found that the magnetization of
an ensemble of CONNECTED rings is of the same order of magnitude as if the
rings were disconnected.
