to Electricity afid Magnetisvi . 511 



sideration the actions of the feeble currents which cannot pass 

 the body, and, consequently, are not concerned in producing 

 the shock, then the same explanation will still apply which 

 was given in the last paper (III. 94-.); namely, in the above 

 example, the helix is acted on by the minus influence of the 

 secondary, and the plus influence of the interposed current. 



85. We are now prepared to consider the effect on the 

 helix (fig. 3.) of the induced currents produced in the con- 

 ductor of the primary current itself. These are true second- 

 ary currents, and are almost precisely the same in their ac- 

 tion as those in the interposed plate. Let us first examine 

 the induced current at the beginning of the primary, in the 

 case of a long coil and a battery of a single element ; its ac- 

 tion on the helix may be represented by the parts of the curve, 

 fig. 20. The first part, A B, will produce an intense induc- 

 tion opposite to that of the primary current ; and hence the 

 action of the two will tend to neutralize each other, and no 

 shock, or a very feeble one, will be produced. The ending 

 action of the same induced current, which is represented by 

 B D, restores to the helix the same quantity of current elec- 

 tricity (but in a feeble state) which was neutralized by A B, 

 and hence the needle of the galvanometer will be as much af- 

 fected as if this current did not exist. These inferences per- 

 fectly agree with the experiment given in paragraph 19. In 

 this, when the ends of the interposed coil v/ere joined so as 

 to neutralize the induced current in the long conductor, the 

 shock at the beginning of the primary current was nearly as 

 powerful as with a short conductor, while the amount of de- 

 flection of the galvanometer was unaffected by joining the 

 ends of the same coil. 



86. At first sight it might appear that any change in the 

 apparatus which might tend to increase the induction of the 

 primary current (16.) would also tend to increase, in the same 

 degree, the adverse secondary in the same conductor; and 

 that hence the neutralization mentioned in the last paragraph 

 would take place in all cases; but we must recollect, that if a 

 more full current be suddenly formed in a conductor of a given 

 thickness, the adverse current will not have, as it were, as 

 much space for its development, and, therefore, will have less 

 power in neutralizing the induction of the primary than be- 

 fore. But there is another, and, perhaps, a better reason, in 

 the consideration, that in the case of the increase of the num- 

 ber of elements of the battery, although the rapidity of the 

 development of the jjrimary current is greater, yet the in- 

 creased resistance which the secondary meets with, in its mo- 

 tion against the action of the several elements, will tend to 



