116 



GRAVITATIONAL METHODS 



[Chap. 7 



Fig. 7-23. Photoelectric cell, amplifier, and transmitter. 



—^ mih^nh 



American Askania Corp. 



Fig. 7-24. Mirror device (Askania) in ampli- 

 fier stage added to receiver. T, transformer; 

 H, horseshoe magnet (end view); M, mirror. 



C M^ 



Fig. 7-25. Amplifier stage with recording 

 glow tube. T, Transformer; C, bias battery; A, 

 battery; B, B battery; MA, milliammeter; G, 

 glow tube. 



hours, or with radio time signals, 

 the chronometer rate is 



The 



plicable. Any inertia in the 

 recording system may be 

 eliminated by a glow-tube 

 oscillograph as shown in Fig. 

 7-25. Its cathode is a 

 slotted cyHnder. The length 

 of the light glow in it is pro- 

 portional to the current. 



D. Instrument Correc- 

 tions IN Pendulum 

 Observations 



Corrections are required 

 in pendulum observations 

 because of (1) variations in 

 the rate of the comparison 

 chronometer, (2) dependence 

 of period on amplitude, (3) 

 temperature, (4) air pressure, 

 and (5) flexure of the sup- 

 port. 



1. The correction for rate 

 of the chronometer is deter- 

 mined by comparing it with 

 astronomical time determi- 

 nations at least every 24 

 pendulum period reduced for 



