270 



MEASUREMENT OF CURRENTS. 



As long as the permanent regime is not established, three kinds 

 of oscillations are produced ; and the form of the experiment gives a 

 period which comprises six oscillations. 



If a, c\ b', b, c, a', a 1 are the successive distances, we have the 

 ratios 



a^a'q. 



The damping being, determined by a series of free oscillations, 



Fig. 170. 



we may deduce several values of the amplitude a from the pre- 

 ceding equations. The most advantageous equations are 



The first is quite independent of the position of zero ; the second 

 only requires a knowledge of zero for terms which are already very 

 small. 



If the damping were so great that we could soon attain a final 

 state, the period would contain no more than three vibrations 



