154 



THE ELECTRIC ARC 



vibrations of the voice. One of the simplest arrangements 

 for this purpose is shown in Fig. 55. A is an arc producing 



FIG. 55- 



oscillations in the circuit ab. M is a microphone producing 

 disturbances in the secondary circuit. P is the primary 

 of an induction coil which is in series with M. S is the 

 secondary circuit of the coil and is in series with the arc. 



The disturbances in P induce 

 currents in S. These currents 

 modify the conditions in the arc 

 and in ab. 



The oscillations produced by 

 S 1 are very much slower than 

 those produced by the arc, so that 

 there will be some groups of waves 

 sent out from ab which are some- 

 what more intense than other 

 groups. The variations in these 

 groups will correspond to the 



FIG. 56. 



vibrations produced in the microphone M. 



A second manner of connecting the microphone is shown 



