32 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



curve, Fig. 20. The first part, A B, will produce an intense induction oppo- 

 site 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 BD, 

 restores to the helix the same quantity of current electricity (but in a feeble 

 state) which was neutralized by ^jB, and hence the needle of the galvanometer 

 will be as much affected 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 were 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 deflection 

 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 con- 

 ductor; 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 before. 

 But there is another, and, perhaps, a better reason, in the consideration that in 

 the case of the increase of the number of elements of the battery, although the 

 rapidity of the development of the primary current is greater, yet the increased 

 resistance which the secondary meets with, in its motion against the action of 

 the several elements, will tend to diminish its effect. Also, by diminishing 

 the length of the primary current, we must diminish (76) the intensity of the 

 secondary, so that it will meet with more resistance in passing the acid of the 

 single battery, and thus its effects be diminished. 



87. The action of the secondary current, in the long coil at the ending of 

 the primary current, should, also, at first sight, produce the same screening 

 influence as the current in the interposed plate; but, on reflection, it will be 

 perceived that its action in this respect must be much more feeble than that of 

 the similar current at the beginning; the latter is produced at the moment of 

 making contact, and hence it is propagated in a continuous circuit of conduct- 

 ing matter, while the other takes place at the rupture of the circuit, and must 



