PEIKCE. 



BALLISTIC GALVANOMETERS OF LONG PERIOD. 



293 



very slight or so strong that the motion is just aperiodic, but in Figure 

 D the lines are drawn to scale for the case u/p = 1/2. 



OEUD is the curve y = e~ x/ ' z • sin x, which reaches its maximum at M. 

 OPFC is the curve y = i ■ e~ x/2 • sin cc, and AFB is the last curve moved 

 to the right through the distance % = ph. The angular deviation of 

 the coil is given as a function of pt by the broken curve OEGH, the 

 ordinates of which are the sums of the corresponding ordinates of 

 OEMD and AFB. The maximum of this curve belongs to a point 



TIME 



Figure D. 



slightly to the left of G and measures the throw of the coil under the 

 circumstances. If both impulses had been given to the coil when it 

 was at rest, the deviation would have been given by the curve OKQGL. 

 The actual throw is about 96 per cent of the throw which would be 

 obtained if both impulses came together at the beginning. The actual 

 values of a and p are not needed, and one does not need to know the 

 period of the coil, the actual intensities of the impulses, or anything 

 else, besides X and r. In this case it is easy to find out by trial in two 

 or three minutes how great the lag OA may be if the difference of the 

 throws is not to be greater than one half per cent, for instance. 



If the secondary of an induction coil which has no iron core be con- 

 nected with the coil of the galvanometer represented by Figure 1, Plate 

 1, and if when the current / is running steadily through the primary 



