Sur les espaces homog enes mod eles de vari et es compactes

A frame for a transparency and a rotatable sound track. The front face of the frame is formed with an annular cavity for rotatably supporting an annular sheet of material having a magnetizable coating and an embossed area forming a spiral sound track on the front face. The annular sheet is supported on a circular wall surrounding an opening through the frame, and the rear face of the frame is provided with a support for positioning a transparency over the opening.