The Williams domain appears in an electroconvective system of nematics under an ac voltage. When the applied voltage is increased, the Williams domain becomes unstable and fluctuates. This state is called fluctuating Williams domain. This instability is caused by the competition between the electroconvective effect and viscous torque. We describe the system size dependence of the appearance of the fluctuating Williams domain. Furthermore, we clarify the properties of the fluctuation from the conductivity and diffusion coefficient by observing the position of fine particles under external forces.
