A conduction model is proposed to explain the electrorheological effec
t under D.C. or low frequency A.C. fields. An approximate analysis tak
ing into account the bulk conduction of the solid and the nonlinear co
nduction properties of the liquid is confirmed by experiments on large
scale spheres. A good agreement between measurements and predictions
is also obtained when air replaces the liquid. Finally the predictions
are extended to the case of surface conduction of the solid spheres.