In this paper, the author shows that, in Tòkyô, the atmospheric oscillation with period of more than eight minutes is generally associated with rain or snow, wave clouds and a surface of discontinuity extends near Tòkyô. The nature of a surface of discontinuity indicating a fairly close relationship with the barometric oscillation was examined in conjunction with the observations by means of pilot balloons and the synoptic charts; and it was concluded that the oscillation is caused by the surface of discontinuity influenced by the topography of Kwantô district. Some theoretical investigations on Helmholtz waves were also undertaken with the object of testing the above conclusions.