Observations have been made of a thin rectangular jet which issues from an orifice and impinges upon the apex of a rigid wedge which is parallel to the plane of the jet. Such a system displays steady motion or motion corresponding to one of a unique set of ordered oscillatory modes. Which state of motion occurs at a given time depends upon stream thickness, orifice‐to‐edge distance, stream velocity, kinematic viscosity, and the previous history of the jet. The investigation is divided into two main parts. One deals with the ranges of parameters of the system for which it will execute self‐maintained oscillations of a given mode; the other treats frequency characteristics for the different modes. It is found that self‐maintained oscillations exist in fluids with a wide range of viscosity. The frequency characteristics are obtained by both optical and acoustical methods; an empirical formula for the frequency is developed.