86 



GRAVITATIONAL METHODS 



[Chap. 7 



In the dynamic method the period of oscillation of the beam is determined 

 with an arrangement shown in Fig. 7-3a and 7-36. The large masses are 

 used first in the extension of the beam and second with their axis at right 

 angles to the beam. Heyl, using masses of 66 kg each for the deflectors, 

 a beam 20 cm long with platinum balls of 54 g each, and a scale distance 

 o^ 3 m, obtained a difference in the two periods of oscillation in the two 

 deflector positions of about 330 seconds. The transits of the beam were 



Fig. 7-36. Torsion-balance arrangement for the determination of the gravitational 



constant (after Heyl). 



recorded on a chronograph, with second signals from a Riefler clock. 

 Heyl reduced the mean error of measurement to ±0.002- 10~* C.G.S., 

 and obtained for k the value of 



k = 6.664 • 10"' C.G.S. 



which is considered the most accurate value now available. 



*♦ Loc. eit. 



