Chap. 7] 



GRAVITATIONAL METHODS 



107 



the pendulum pair and the chronometer is very slight. If the period of 

 chronometer and pendulum pair were exactly alike, the chronometer 

 breaks would always occur at the same relative positions in the pendulum 

 curves and the phase-lag-sine curve passing through the breaks would be 

 a straight line. If the period 



/T/\A-A'/riV,(A-'/\711A 



of the pendulum pair is greater 

 than the chronometer interval, 

 the chronometer breaks occur 

 at intervals less than a com- 

 plete cycle (or | cycle). The 

 sine curve of the breaks is 

 therefore an expression of the 



w 



wmmw 



Fig. 7-14. Vening Meinesz pendulum record 

 (schematic). 





iiilliiil 



Fig. 7-15. Photographic record of Vening Meinesz pendulum apparatus. Upper 

 record: First fictitious pendulum with marks of two chronometers. Middle record: 

 Second fictitious pendulum with chronometer marks and record of air temperature 

 and of auxiliary damped pendulum 1, recording the tilt angle. Lower record: Record 

 of pendulum 2 recorded with reference to auxiliary damped pendulum 2. (The latter 

 swings in the plane of oscillation of the regular pendulum while auxiliary damped 

 pendulum 1 swings at right angles to that plane.) 



receding movement of the pendulum vector whose angular velocity is the 

 phase lag of the pendulum pair. 



The evaluation of the record is made as follows. By an automatic 

 mechanism a mark is left ofi every 60 seconds on the record (for instance, 

 before A in Fig. 7-14) . In determining the time of passage of the phase-lag 



