Chap. 7] 



GRAVITATIONAL METHODS 



193 



nificance. A detailed description with instrument constants has been 

 given by Jung.^^ In 1888 and 1890, respectively, Eotvos constructed the 

 first curvature and combined curvature and gradient variometers for 

 laboratory use. In 1898 he followed this with a combined single beam 

 field instrument. Its dimensions and constants were (in round figures): 

 m (single beam mass) = 30 g, /i (distance of weights) = 60 cm, I (^ beam 

 length) = 20 cm, K (moment of inertia) = 21,000, r (torsional coefiicient 

 of suspension wire) = 0.5, d (thickness of wire) = 40/i, L (length of wire) = 

 56 cm. These dimensions have been maintained by all designers of large 

 visual and automatic torsion balances. 



Fig. 7-65. From left to right: small Suess balance, large Suess balance, small Asiania 



balance. 



The single balance was replaced in 1902 by a double variometer (see 

 Fig. 7-65) with visual observation. Most large instruments developed 

 after that, such as the Fechner, Oertling, and Askania (see Fig. 7-66) 

 balances, used photographic recording devices and automatic azimuth 

 rotation. Repeated attempts were made to reduce the dimensions of the 

 large torsion balance. Eotvos himself went to the extreme with an in- 

 strument in which m = lA g„ h = 20, I = 5, K only 90, and r = 0.0046; 

 but this instrument was a failure. Similar in dimensions was the Tsuboi 



" K. Jung, Handb. Exper. Phys., 25(2), 103-123 (1930). 



