1840] WRITINGS OF JOSEPH HENRY. 181 



ceed 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 development must be greater than that 

 of their diminution, and, consequently, they may be repre- 

 sented by a curve of the form exhibited in Fig. 20, in which 



^ -i C 



Fig. 20. 



there is no constant part, and in which the steepness of ^ -S 

 is greater than that of B C. There are however other con- 

 siderations, which will be noticed hereafter, (89,) which may 

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



79. It will be seen at once, by an inspection of the curve, 

 that the effect produced in a third conductor, and which we 

 have called a tertiary current, is not of the same nature as 

 that of a secondary current. Instead of being a single de- 

 velopment in one direction, it consists of two instantaneous 

 currents, one produced by the induction of A B, and the 

 other by that of B C, in opposite directions, of equal quan- 

 tities, but of different intensities. The whole quantity of 

 induction in the two directions, will each be represented by 

 the ordinate B b, and hence they will nearly neutralize each 

 other, in reference to their action on the galvanometer, in 

 the circuit of the third conductor. I say they will nearly 

 neutralize each other, because, although they are equal in 

 quantity, they do not both act in absolutely the same mo- 

 ment of time. The needle will therefore be slightly af- 

 fected ; it will be impelled in one direction — say to the right, 

 by the induction of A B, but, before it can get fairly under 



