142 



W. D. Lambert — Mechanical Curiosities 



in the meridian and the prime vertical, as we have been 

 supposing. The directions of maximum and minimum 

 curvature are also found by the balance. These curva- 

 tures may be interpreted in terms of the second deriv- 

 atives of Y, the potential function of the gravity field. ^^ 

 If we take rectangular axes, the ^-axis being vertical at 

 the center of the balance, an instrument of the first type 

 will give the numerical value of 



The Eotvos balance of the second type has its masses 

 at the two ends of the rod at different levels, the counter- 

 poise of the one loaded end of the bar being a suspended 

 weight (see ^g. 6). Without going into details it may be 

 said that this balance brings into play forces derived from 

 the change in the direction of gravity with elevation, 



and 



of ^- 



9x 9y 



Fig. 6. 



fZ 



I 



Fig. 6. — Schematic form of the Eotvos balance, second type. 



-^ See references in footnote on a preceding page. 

 Art. A, p. 355. 

 Art. I, p. 317 or Helmert, Hohere Geodasie, Vol. II, pp. 35-40. 



