Abstract: The present invention is directed to a window assembly comprising (a) a frame having opposed, vertical jambs with an upper sash guide rail, joined at their ends to the ends of opposed, horizontal top and bottom members forming, respectively, a header and a sill; (b) an upper and lower window sash, with the upper sash having stiles extending into the guide rails in the jamb to enable vertical sliding movement of the upper sash in the frame; (c) a parting rail mounted to the upper portion of each jamb in a channel adjacent to the upper sash guide rail to retain the upper sash within the frame, each parting rail having a longitudinal dimension about equal to the longitudinal dimension of the upper sash; (d) a parting rail spring means mounted in each channel to push the parting rail away from the jamb and towards the sash to hold the upper sash in place; and (e) a parting rail activator mounted on the upper outer edge of each upper sash; wherein the parting rail activator engages the parting rail when the upper