28 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



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 re- 

 ference 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 in- 

 stant, of the natural electricity of the metal, which, subsiding, leaves the con- 

 ductor 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 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 gene- 

 rated, and also, perhaps, in some degree, 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 produces the se- 

 condary current to be sufficiently intense, the velocity of its development will 

 exceed that of its diminution, as in the example of the primary current from 

 the intense source of the compound battery of many elements. Now this is 

 the case with the inductions which produce currents of the different orders, 

 capable of giving shocks or of magnetizing steel needles ; the secondary currents 

 from these are always of considerable intensity, and hence their rate of develop- 

 ment must be greater than that of their diminution, and, consequently, they 

 may be represented by a curve of the form exhibited in Fig. 20, in which there 



is no constant part, and in which the steep- 

 ness of A B is greaterthan that of B C. There 

 are, however, other considerations, which 

 will be noticed hereafter, (89,) which may 

 affect the form of the part B C of the curve, 

 Fig. 20, rendering it still more gradual in its descent, or, in other words, which 

 tend to diminish the intensity of the ending induction of the secondary current. 



