176 WRITINGS OF JOSEPH HENRY. [1840 



gradual development of the current in the short conductor, 

 with a single battery, and the gradual decline of the same, 

 are represented by the gentle rise of A B and fall of C D, 

 Fig. 18; while, in the next Fig., (19,) the sudden rise of AB 

 indicates the intensity which produces the increased shock, 

 after the number of elements of the battery has been 

 increased. The accumulation of the electricity, which 

 almost instantly subsides, is represented by the part Bee, 



Fig. 19. 



Fig. 19, and from this we see, at once, that although the 

 shock is increased by using the compound battery, yet the 

 needle of the galvanometer will be deflected only to the 

 same number of degrees, since the parts Be and ce give 

 inductive actions in contrary directions, and both within 

 the time of the single swing of the needle, and consequently 

 they will neutralize each other. The resulting deflecting force 

 will therefore be represented by ef, which is equal to C k, 

 or to b B, in Fig. 19. The intensity of the shock at the 

 breaking is represented as being the same in the two figures, 

 by the similarity of the rate of descent of the part C D of the 

 curve in each. 



71. We have said (69) that the quantity of current elec- 

 tricity in a short conductor and a compound battery, after 

 the first discharge, is nearly the same as with a single bat- 

 tery. The exact quantity, according to the theory of Ohm, 

 in a unit of length of the conductor, is given by the formula — 



nA . 

 rn -i- R 



In this, n represents the number of elements; A, the elec- 

 tro-motive force of one element; r, the resistance to conduc- 

 tion of one element ; and R, the length of the conductor, or 

 rather, its resistance to conduction in terms of r. Now when 

 R is very small in reference to r n, as is the case with a very 



