1838] WEITINGS OF JOSEPH HENRY. 143 



130. The neutralizing effect described in Section iv may 

 now be more definitely explained by saying that when a 

 third conductor is acted on at the same time by a primary 

 and secondary current (unless it be very near the second 

 wire) it will fall into the region of the plus influence of the 

 former, and into that of the minus influence of the latter ; 

 and hence no induction will be produced. 



131. This will be rendered perfectly clear by Fig. 15, in 



which a represents the conduc- 

 'j^ tor of theprimary current, 6 that 



+ , of the secondary, and c the third 



-I- 4- conductor. The characters + + 



+ -2. -j-, &c., beginning at the mid- 



_)- _ die of the first conductor and 



extending downwards, represent 

 the constant plus influence of 

 + ~~ the primary current, and those 



^^°- 1^- +0 , &c., beginning at the 



second conductor, indicate its inductive influence as chang- 

 ing with the distance. The third conductor, as is shown by 

 the figure, falls in the plus region of the primary current, 

 and in the minus region of the secondary, and hence the 

 two actions neutralize each other, and no apparent result is 

 produced. 



132. Fig. 16 indicates the method in which the neutra- 



lizing effect is produced in the 



^ case of the secondary and terti- 



^ ary currents. The wire conduc- 



^ ^ ting the secondary current is 



— + represented by b, that conduct- 

 ^ _ ^ ing the tertiary by c, and the 



other wire, to receive the in- 

 ~ + duction from these, by d. The 



— + direction of the influence, as be- 

 ^iQ- 19- fore, is indicated by + , 



&c,and the third wire is again seen to be in the plus region 

 of the one current, and in the minus of the other. If how- 

 ever d is placed sufficiently near c, then neutralization will 



