On Electro-Dynamic Induction. 145 
of the twenty feet of the primary current would severally pro- 
duce an inductive action of the same intensity as that of the 
short conductor, the velocity of collapsion being the same; and 
as they are all at once exerted on the same conductor, a secon- 
dary 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 conductor; hence, the action 
of the several units of length of the primary current must 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. 
e may next consider the character of the secondary cur- 
rent, in reference to its action in producing a tertiary current in a 
third conductor. ‘The secondary current consists, as we may 
Suppose, in the disturbance, for an instant, of the natural electri- 
city 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 dura- 
tion, and that it increases, by degrees, to a state of maximum 
development, 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 de- 
gree, on the resistance of the conductor; while, agreeably to the 
hypothesis we have assumed, (69,) the velocity of its diminution 
is nearly a constant quantity, and is not affected by changes in 
these conditions; hence, if we suppose the induction which pro- 
duces the séebndlii’y current to be sufficiently intense, the velo- 
nution 
Vol. xx, No. 1.—April-June, 1841.’ 19 a 
