Shock waves propagating through sec‐butyl alcohol and carbon tetrachloride vapor produce condensation of the vapor molecules on the shock‐tube walls in the form of a thin liquid film. Electrostatic voltage changes in the potential of narrow metal foils wrapped around the outside of a glass shock‐tube section are associated with the passage of the shock wave through the vapor. The electrostatic signals have been attributed to the shear at, or in the liquid film, due to the presence of the laminar vapor boundary layer established by the shock. The observed signals are consistent with a cylindrical sheet of positive charge which originates at the shock and extends behind the shock for a length equal to that of the laminar boundary layer.