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TENTH ANNUAL REPORT OP 



This method is too laLoiions for general use. 



Thus, methods for determining the constants of the battery (elec- 

 tro-motive force and resistance) were sought for, which do not require 

 the knowledge of the force of the current. These efforts were even 

 continued after Pouillet's and Weber's tangent compass, as well as 

 the compass of sines, were known. It is really surprising that such 

 important instruments as these, which introduced so great simplicity 

 into the study of galvanic laws, were so slowly adopted and so gener- 

 ally applied. 



We shall now consider more closely the best of these indirect 

 methods. 



Jacobi presents the following : (Pogg. Ann. LVIIl, 85.) The 

 Pi„ n conducting circuit of the battery i» 



divided into two parts, as shown in 

 Fig. 11. Let the resistance to conduc- 

 tion of one of the branches be L, that 

 of the other I, in which the rheostat* is 

 inserted at a, the galvanometer at b; 

 then the resistance which these two cir- 

 cuits, inserted at the same time, pro- 

 duce, is — 



I L 



Hence, the whole force of the current 

 which the apparatus yields is — 



S 



_ E (L 4- 



^ (^ + L) -f- ^ L * 



Denoting, by )., the resistance of the elements, (including the conduc- 

 tor between m and «.) 



The part of the entire current which passes through the galvano- 

 meter is — 



q; E L 



~ /({L-\-l) -^l L' 

 Breaking the lateral closing, the force of the current in the other 

 circuit will increase, and we must add the resistance x by means of 

 the rheometer^ to restore the galvanometer needle to its former posi- 

 tion; but we have now for the force of S' the value — 



S' 



E 



From this and the previous equation we get for X the value — 



, xJj 



Now, since x, L and I are known, the resistance of the elements can 

 be determined by this method, without knowing the value of the force 

 of current. 



» An account of this instriunent is given at the close of this section. 



