1840] WRITINGS OF JOSEPH HENRY, 185 



Its action on the helix may be represented by the parts of 

 the curve, Fig. 20. The first part, A B, will produce an in- 

 tense induction 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 electricity (but in a feeble state) which was neu- 

 tralized by A B, and hence the needle of the galvanometer 

 will be as much affected as if this current did not exist. 

 These inferences perfectly 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 pri- 

 mary current was nearly as powerful as with a short con- 

 ductor, while the amount of deflection of the galvanometer 

 was unaffected by joining the ends of the same coil. 



8G. At first sight it might appear that any change in the 

 apparatus which may 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 recol- 

 lect that if a more full current be suddenl}'' formed in a con- 

 ductor of a given thickness, the adverse current will not 

 have as much space as it were for its development, and 

 therefore will have less power in neutralizing the induction 

 of the primary than before. But there is another and per- 

 haps 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 (7G) 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. 



