SYNCHRONIZED SOUND PICTURES 



191 



ducing the condenser C2 in series with the high resistance Ri. When a 

 change in current through the regulating reactance Li occurs the 

 corresponding change in voltage drop is not transmitted to the con- 

 denser Co immediately, but C2 changes its voltage after a certain 

 time lag (approximately 1 second), required to charge the condenser 

 through the resistance R4. The introduction of this time lag restores 

 the precision of the circuit to the flat characteristic desired without 

 introducing hunting. 



Variable Speed Operation 



By throwing the switch Si to the right the operator can disconnect 

 the tuned circuit control and substitute a potentiometer Pi as a 



Fig. 8 — D. C. motor with control cabinet. 



source of grid voltage for tube V4. By means of this potentiometer 

 the operator can adjust the speed of the motor at any speed from 

 900 to 1,500 R.P.M. corresponding to 68 to 112 feet of film per minute. 

 This feature is employed for ordinary motion picture work where it is 

 unnecessary to synchronize the picture with the sound. The regu- 

 lation of the circuit under these conditions is sufiiciently good for 

 ordinary motion pictures. 



An interesting feature in this connection is that theaters in many 

 cases have preferred to use the regulated speed position for ordinary 

 motion pictures as well as synchronized pictures. The reason for 

 this being that with the speed of the projector precisely controlled 

 the orchestra leader is better able to keep his orchestra in step with 

 the picture indicating apparently that closer speed regulation than is 



