Electric Arc between a Ball and Point. 



127 



variometer g, it measured the fall of potential through the 

 coils of the latter instrument. The function of the indicating 



Fijr. 1 



galvanometer, during this part of the investigation, consisted 

 in showing, by the size and direction of its deflexion, whether 

 the discharge between the ball and point continued to main- 

 tain its proper character. 



The result of measurements throughout a complete cycle, 

 both when the arc was formed and when it was extinguished, 

 is shown in curves B and A (fig. 2). Curve A is with close 

 approximation a curve of sines, and it indicates the usual 

 fluctuations of current to be looked for in the secondary circuit 

 of an alternating system. Curve B shows the current through- 

 out the cycle when the arc was playing. Abscissae represent 

 portions of a complete cycle, the period being divided into 

 twenty equal parts, ordinates the relative amounts of current 

 through the resistance K, or the total current in the secondary 

 circuit. Deflexions, when the current flows from ball to point, 

 are plotted above the base line. As may be seen from the 

 curve B, the current flowing in the positive direction during 

 each cycle was greatly in excess of that flowing in the nega- 

 tive direction, when the discharge was taking place between 

 ball and point, whereas when no arc was formed (curve A) the 

 areas inclosed by the positive and negative branches of the 

 curve were equal. Now there were two paths offered to the 

 current, that through the galvanometer g and the resistance 



which consisted of 



column of copper-sulphate 

 L2 



solution 



