E. L. Nichols — Alternating Electric Arc. 5 



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 R, or the total current in the secondary 

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



/ // \c \ \ 



--"\ 



— ■ ** — ■ ■ ■ ■■ / ■ *• — - 



I 2 M 4 & 6 7.// 9 ,.. „ N 



\ / /'' If i N 



y/ 



\ F 



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 enclosed 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 r, 

 which consisted of a column of copper-sulphate solution between 

 copper poles (approximately 112000 ohms), on the one hand, 

 and the parallel circuit between the ball and point on the other. 

 The resistance of the latter path was infinite whenever the arc 

 was interrupted, falling to finite values during each discharge. 

 Increase of current through R indicates, therefore, the forma- 

 tion of the arc. Such increase is found to exist during the 

 second half of each cycle, that is to say, during that interval in 

 which the ball is positive ; and it might be inferred from these 

 curves alone that the discharge was an intermittent one taking 

 place always from ball to point. Other curves, taken simulta- 

 neously with A and B, the Thomson galvanometer being 

 shunted around the indicator galvanometer, lead to the same 

 conclusion. The curves marked C and D (figure 2), show the 



