GRAVITATIONAL METHODS 



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The sensitivity of the balance is about 0.46 Eotvos units per 0.1 of a 

 scale division of the graduated plate. 



Z-Beam Torsion Balance 



In the Z-beam torsion balance (Figure 163) the end portions of each of the balance 

 beams are bent so as to form right angles, and the weights are rigidly attached to the 

 extremities of the vertical parts. With one weight above the balance beam and the 

 other below it, the center of gravity of the suspension system is about 2 cm. above the 

 beam. The small equal weights have a mass of about 22 g. and the distance between 

 them h is 45 cm. 



The base and central section are identical with those of the large torsion balance, 

 except that the base consists of one piece. The overall height of the Z-beam torsion 

 balance, however, is only 120 cm. (47 in.) 

 and its weight when set up is 104 pounds. ^ 



The observation period or time for the 

 balance beam to come to rest is 40 minutes. 

 The sensitivity is about 0.6 Eotvos units 

 per 0.1 of a scale division of the graduated 

 plate. 



The Z-beam torsion balance has been 

 used for investigations of geologic struc- 

 ture and tectonic problems, and for locat- 

 ing salt domes, anticlines, and faults. 



Torsion Balance with Inclined Beams 



The central section and base of this 

 instrument are similar to those of the 

 large torsion balance and the Z-beam tor- 

 sion balance except that the upper plate 

 of the central section is designed to cor- 

 respond with the base of the upper sec- 

 tion. The center of gravity of the sus- 

 pension system is 90 cm. above the base 

 plate. The overall height of the inclined 

 balance is 126 cm. (50 in.), and its weight 

 when set up is 82 pounds. 



An exterior view of the instrument 

 is shown in Figure 164. The upper section 

 of the inclined beam balance differs fun- 

 damentally from that of the large and Z- 

 beam balances. It comprises a central 

 casing for the optical system and two cas- 

 ings for the balance beams. Each of the 

 balance casings can be removed indepen- 

 dently of the other. The balance casings 

 are double-walled as a protection against 

 temperature changes, and each contains a 

 torsion wire and torsion head in addition 

 to the inclined balance beam. The torsion 

 wire is 260 mm. long. The small masses 

 weigh 40 g. each, the horizontal distance 

 between them is 20 cm. and the vertical 

 distance is 30 cm. The prism support is 

 connected to the balance beam by a bifilar „ , ., _ . , , •.■, • i- j u „. 



, . , 1 • 1 -I Fig. 164. — Torsion balance with inclined beams, 



suspension which prevents the axial OSCll- (Courtesy of American Askania Corporation.) 



