“…( 1 )), the principles of their drainage still are not fully understood. Drainage has been studied extensively in the case of horizontal films (2-4); however, investigations of vertical films focused on Frankel's law for film formation ( 1,(5)(6)(7)(8), black films (9-21), bursting (22)(23)(24)(25), film contact angles (26)(27)(28)(29)(30)(31), and surface waves (32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42), the last subject being treated mainly theoretically. Only a few papers dealt with actual flow in free films (10,(43)(44)(45) and Plateau borders (46), but the physics of the main drainage mechanism for mobile films, viz., marginal regeneration (1, 7), remained unsolved.…”