The Blake transmitter takes its name from the inventor of its mechanical features, who has assembled in it the fundamental principles of Berliner and Edison in a sensitive and practical mechanical construction, covered by minor patents, dated November 29, 1881. It is the little box in the middle of the familiar telephone outfit into which the talking is done. Its internal construction is shown in Fig. 59. To the rear of the door is secured the cast iron circular ring A, inside of which lies the Russia iron diaphragm B, cushioned at its edges with a rubber band. A circular seat a little larger than the diaphragm is formed in the iron ring, and on this seat the diaphragm rests. A short, thin metal plate attached to the ring A on the right hand side clamps the diaphragm in position by resting squarely on the rubber edge of the diaphragm. Its function is like that of a hinge, which allows the diaphragm to freely swing inward. A steel damping spring is secured to the ring at the opposite edge of the diaphragm, and has its free end provided with a rubber glove on which is cemented a thin piece of fluffy woolen material. The padded end of the damping spring rests against the diaphragm and prevents excessive vibration. The iron ring A has at its bottom a projection holding an adjusting screw, and to a similar top projection is attached by screws a brass spring, from which depends another casting C, supporting the microphone apparatus, which is best shown in the diagram, Fig. 60. In this diagram A is one terminal of the battery connected by wire S to the hinge H of the box. From the other leaf of the hinge the wire M passes to K, where it is soldered to the upper end of a German silver spring I. At K this spring is clamped and insulated from the iron work by two pieces of hard rubber. On the lower end of the spring I is soldered a short piece of thick platinum wire, whose ends are rounded into heads, one of which bears against the diaphragm N, and the other against the carbon button J. This button is attached to a small brass weight, and is supported by a spring R, clamped at its upper end to the metal support T. This spring is surrounded its entire length by rubber tubing to deaden vibration. The transmitter is adjusted by screw O, which, acting upon casting T, brings the carbon button, the platinum heads, and also the diaphragm N, against each other with a regulated pressure. The current passes from the part K to the spring I, the platinum head, carbon button J, and its supporting spring R, to metal casting T, and ring V, thence by wire L to the lower hinge G, by wire P to the primary of the induction coil, and thence by wire Y to binding post B, the two binding posts A B being the two battery terminals. The secondary wire E of the induction coil has its ends connected by wires X and W with the two binding posts C B, which are the line terminals, or one the line terminal and the other the ground connection.