THE BALLISTIC GALVAXOMETEK ILV) 



The moving coil is hung by a silk fiber from the spring support 

 I\; the current is led to the coil through the delicate spirals S, S, 

 which are of annealed silver and supposed to exercise no eon trol- 

 ling effect on the movable system. A mechanical device is em- 

 ployed by which the system may be quickly reset to its zero 

 position. 



The instrument is used in series with an exploring coil and 

 therefore in a closed circuit. When the change of flux through 

 the test coil is completed, the movable system comes to rest in its 

 deflected position and the change in linkages is given by 



n = C0i (40) 



which is true, irrespective of the manner in which the Hux is 

 changed and of the time occupied in making the change. This 

 connection between the deflection and the change of ilux linkages 

 may be seen from equation (12). 



When the torsional control, r, is indefinitely reduced, tn\ and 

 w-j which arc the roots of the equation Pnr -f- km -f r = 

 approach the values 



///i =0 



k 



Under these conditions (gee page 112). 



M = 1, 



N = sonic definite numerical value. 



m\ mi 



and the factor A"" in (12), which depends on the 



manner in which the discharge takes place, always becomes 

 unity. The factor in (12) which is within the brackets also 

 approaches unity, so if n is the total change of flux linkages 



ta 



C 2 



k = -f //, see page 1 10. 

 n = (c + c , r ) 0L 



