  The experimental critical temperature of systems of nanoparticles
superconducting (Pb) and normal (Ag, Cu and Al) with a random distribution and
sizes less than their respective coherence lengths, is governed by proximity
effect as the experimental data shown. At first glance the behaviour of the
variation of the critical temperature in function of the ratio of the volume
fractions of the superconducting and the normal metal components seems to
suggest a weak coupling behaviour for the superconductor. In reality, upon a
more careful analysis using Eliashberg's theory for the proximity effect, the
system instead shows a strong coupling nature. The most interesting thing is
that the theory has no free parameters and perfectly explains the behavior of
the experimental data just with the assumption, in the cases of nanoparticles
of $Ag$ and $Cu$, that the value of the density of states at the Fermi level of
silver and copper is equal to value of lead.
