REFERENCE SYSTEM FOR TELEPHONE TRANSMISSION 545 



Fig. 4 and in cross-section in Fig. 5, a thin highly stretched duralumin 

 diaphragm is mounted close and parallel to a steel plate grooved and 



Fig. 4 — Condenser transmitter and moving coil receiver. 



perforated for air damping. This diaphragm and plate form the 

 electrodes of a condenser polarized by a battery through a high 



GOLD LEAF STRIPS 

 WIDTH OF EACH 1 CM- 



'CONTACT SURFACES 



^CAPILLARY TUBES 

 FOR HYDROGEN 



Fig. 5 — Schematic of condenser transmitter and thermophone. 



resistance. Sound vibrations impinging on the diaphragm actuate it 

 and produce variations in the capacity of this instrument. The 



