Solid Angle

—The angle made by the intersection of three plane surfaces at one point. Solid Back Transmitter.--A modern form of telephone transmitter so called because the back electrode is rigidly supported by the frame of the instrument. The front is very stiff, having the hard rubber mouthpiece screwed into it. The diaphragm of aluminum lies just back of the front with a rubber band snapped over it to provide an insulated cushion seat for the diaphragm. The two electrodes are carbon discs, the space between them being partially filled with carbon granules. The vibrations of the diaphragm are transmitted to the front electrode by a pin which makes a rigid connection between them.