Аннотация
The dispersion equation for capillary motions for inviscied twolayer fluid acted by gravity is derived and investigated both analytically and numerically when there is a charge on the interface of the layers and when upper layer move along the interface. It was supposed that an upper layer thickness is finite but uderlayer has an infinite depth. The characteristic property of the Tonks-Frenkel instability and the Kelvin-Helmholtz instability are investigated.