  The diamagnetism of a normal metal (N: Cu or Au), which is induced by the
proximity effect of a superconductor (S: Nb), has been investigated for N-S
double layers, which are formed by a thin-film deposition process. Detailed
studies of samples, which have different electronic mean-free path \ell_N in N,
suggest that \ell_N should be controlled by the impurity concentration rather
than the mechanical imperfections in the lattice in order to clarify the \ell_N
dependence of the proximity effect. Both the screening distance \rho in N and
the parameter \nu in \rho \propto T^-\nu increase with an increase in \ell_N.
This result can be understood on the assumption that the normal metal changes
its behavior from the "dirty" limit (\xi_N>\ell_N) to the "clean" limit
(\xi_N<\ell_N), where \xi_N is the coherence length in N.
