  Watts and Strogatz [Nature 393, 440 (1998)] have recently introduced a model
for disordered networks and reported that, even for very small values of the
disorder $p$ in the links, the network behaves as a small-world. Here, we test
the hypothesis that the appearance of small-world behavior is not a
phase-transition but a crossover phenomenon which depends both on the network
size $n$ and on the degree of disorder $p$. We propose that the average
distance $\ell$ between any two vertices of the network is a scaling function
of $n / n^*$. The crossover size $n^*$ above which the network behaves as a
small-world is shown to scale as $n^*(p \ll 1) \sim p^{-\tau}$ with $\tau
\approx 2/3$.
