BALANCE MAGNETOMETEK. 199 



supposed to be connected with the magnet, and to 

 vibrate with it. Let V be the magnet-power of earth's 

 vertical force, B the magnet-power of the magnet; 

 then as in Article 21, the angle 6 being very approxi- 

 mately 90, 



V.B=WxKGi 



K being in the vertical below C, not vibrating with the 

 magnet. It will be remembered that, in that Article, 

 the units of statical and dynamical forces are connected 

 by a formula which does not contain g. 



Now suppose the Earth's vertical force V to vary. 

 The only other element in the last equation which can 

 vary is KG. Hence we find 



and, dividing this by the preceding equation, 



= 

 v KG 



But, as we cannot immediately measure S . KG, we 

 must resort to an indirect process in order to extract 

 a meaning from this equation. If the magnet is in- 

 clined through the small angle ty, S. KG will = CKx \jr, 

 and 



SF CK 



Now a value of CK may be obtained by causing the 

 magnet to vibrate on its knife edges, thus. Let / be 



