  The thermodynamics of electrowetting is treated. A general equation of
electrowetting is derived from the first principles. It is demonstrated that
the well-known Lippmann Equation describes a particular case of electrowetting
when the radial derivative of the capacitance of the double layer is constant.
The apparent contact angle of electrowetting depends on the gradient of
capacity of a double layer in the vicinity of the triple line. The role of the
area adjacent to the triple line in constituting the equilibrium apparent
contact angle of electrowetting is emphasized.
