90 BELL SYSTEM TECHNICAL JOURNAL 



events under observation have been recorded the starting lever is 

 pushed back, withdrawing the idler pulley from the main drive roll, 

 and releasing the knife, which cuts off the exposed section of paper. 

 An electromagnetic brake, operated by a timing control circuit, is 

 momentarily applied to the spinning roll of paper, and stops it in a 

 fraction of a revolution. The exposed paper continues to pass through 

 the developing and fixing tanks, and into the rinsing tank until it has 

 all been developed. A view of the machine with the developing and 

 fixing tanks dropped for inspection of the mechanism is shown in 

 Fig. 12. A solenoid may be provided for operating the machine from 

 a distance when desired. 



The complete galvanometer element of the three-string model is 

 shown in Fig. 13, and one pole piece and the string mounting, in Fig. 14. 



As an illustration of the many uses of the new oscillograph, an oscil- 

 logram is given in Fig. 15, which shows the wave form of the sound 

 radiated from the gong of a telephone ringer struck once by the clapper. 

 The sound was picked up by a dynamic type microphone, and the 

 resulting current was amplified and fed to a rapid record oscillograph 

 tuned to 4000 cycles and equalized to 7500. The entire system was 

 reasonably distortionless from 30 to 8000 cycles per second. It is 

 interesting to note that the predominant frequency, about 6000 cycles 

 per second, would not have been detected had the record been made 

 with the older types of oscillographs. 



