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BELL SYSTEM TECHNICAL JOURNAL 



galvanometer and tracing the scale and frequency lines, and suitable 

 baths for de\eloping and fixing the record. The record is drawn 

 through the mechanism by means of two motor-driven rubber rollers, 

 which also serv-e to remove excess solution. 



The development of the pneumatic switching apparatus was carried 

 out with a view to making use of as many standard piano player 

 parts as possible. However, it was found necessary to make some 



DIAPHRAGMS 



A\R COMPAtrrMEETTS 



Fig. 4 — Piifiiniatic Relay 



modifications in method and apparatus; in particular a new pneu- 

 matic motor element (air relay) for switching the condensers at the 

 requisite speed had to be developed. 



Fig. 3 is a schematic drawing showing the principal features of 

 the analyzer. In this drawing the vacuum pump is shown driven 

 by an electric motor, and connected by means of pipes to the auxiliary 

 and main headers and relays. This pump maintains in the headers 

 an absolute pressure of about 4 or 5 H). per square inch. The player 

 piano roll E operates the entire mechanism by passing over the 

 tracker bar in the usual manner. The air motor and tracker bar 

 equipment are substantially as supplied by the manufacturers except 

 that the reversing mechanism is arranged to be operated electrically 

 instead of by hand. 



The essential features of the air relay which was developed for 

 this analyzer may be better understood by reference to Fig. 4. A 

 cylindrical casting is arranged to mount two flexible diaphragms and 



