  Starting with an expression, due originally to Einstein, for the shear
viscosity \textit{$\eta $}(\textit{$\delta \phi $}) of a liquid having a small
fraction \textit{$\delta \phi $}by volume of solid particulate matter suspended
in it at random, we derive an effective-medium viscosity \textit{$\eta
$}(\textit{$\phi $}) for arbitrary \textit{$\phi $} which is precisely of the
Vogel-Fulcher form. An essential point of the derivation is the incorporation
of the excluded-volume effect at each turn of the iteration \textit{$\phi
$}$_{n + 1 =}$\textit{$\phi $}$_{n}$\textit{+$\delta \phi $}. The model is
frankly mechanical, but applicable directly to soft matter like a dense
suspension of microspheres in a liquid as function of the number density.
Extension to a glass forming supercooled liquid is plausible inasmuch as the
latter may be modelled statistically as a mixture of rigid, solid-like regions
(\textit{$\phi $}) and floppy, liquid-like regions (1-\textit{$\phi $}), for
\textit{$\phi $} increasing monotonically with supercooling.
