208 



GRAVITATIONAL METHODS 



[Chap. 7 



pedestal is placed in position on the aluminum base plate. This is followed 

 by the center piece, which in the automatic instruments is provided with 

 stops for three, four, and five positions and which must be set according to 

 the azimuths selected. The upper part of the instrument containing the 

 beams is secured in place, and tubes for the hanging weights are attached 

 where necessary. 



After the instrument has been assembled, it is carefully leveled. In 

 automatic balances the driving clockwork is wound and engaged and the 

 upper part allowed to rotate until it reaches the first stop. The compass 



Table 29 

 CALCULATION OF FIVE-POSITION TORSION-BALANCE RECORD 



(FROM n's) 



Part 1 



needle is then released and the upper part, together with the turntable, is 

 turned clockwise until the side of the balance case is in the astronomic 

 meridian. After the beams have been released, a visual instrument is 

 ready for observations in the first and all other azimuths at about 50- 

 minute intervals. In an automatic instrument a plate must be inserted, 

 the recording clock wound, and a trial run made before the instrument 

 can be left to itself. Further details are given in the author's torsion- 

 balance manual.* 



" Directions for the Askania Torsion Balance. 



