180 WRITINGS OP JOSEPH HENRY. [1840 



produce an inductive action of the same intensity as that 

 of the short conductor, the velocity of collapse being the 

 same ; and as they are all at once exerted on the same con- 

 ductor, a secondary current would result of twenty times the 

 intensity of the current in the former case. 



77. To render this explanation more explicit, it may be 

 proper to mention that a current produced by an induction 

 on one part of a long conductor of uniform diameter, must 

 exist of the same intensity in every other part of the con- 

 ductor ; hence, the action of the several units of length of 

 the primary current must re-enforce each other, and produce 

 the same effect on its own conductor that the same current 

 would if it were in a coil, and acting on a helix. I need 

 scarcely add, that in this case, as in that given in paragraph 

 74, the whole amount of induction is greater with the long 

 conductor than with the short one, because the quantity of 

 current electricity is greater in the former than in the latter. 



78. We may next consider the character of the secondary 

 current, in reference to its action in producing a tertiary 

 current in a third conductor. The secondary current con- 

 sists (as we may suppose) in the disturbance for an instant of 

 the natural electricity of the metal, which subsiding leaves 

 the conductor again in its natural state ; and whether it is 

 produced by the beginning or ending of a primary current, 

 its nature, as we have seen, (22,) is the same. Although 

 the time of continuance of the secondary current is very 

 short, still we must suppose it to have some duration, and 

 that it increases, by degrees, to a state of maximum develop- 

 ment, and then diminishes to the normal condition of the 

 metal of the conductor ; the velocity of its development, like 

 that of the primary current, will depend on the intensity of 

 the action by which it is generated, and also perhaps in 

 some degree, on the resistance of the conductor ; while, agree- 

 ably to the hypothesis we have assumed, (69,) the velocity of 

 its diminution is nearly a constant quantity, and is not af- 

 fected by changes in these conditions ; hence, if we suppose 

 the induction which produces the secondary current to be 

 sufficiently intense, the velocity of its development will ex- 



