1888.] 



NATURAL SCIENCES OF PHILADELPHIA. 



157 



the preceding experiment that the vertical line A E Fig. 3 repre- 

 sents the electro-motive force of the current as it enters A Fig. 1 

 from the Daniell and that the horizontal line A S B Fig. 3 represents 

 the resistance offered by the wire A S B Fig. 1, S representing in 

 Fig. 3 the point where the current passes into the galvanometer 

 from S in Fig. 1, S G in Fig. 3 will then represent the electro-motive 

 force of the current at the point S. It need hardly be added that 

 S G must be shorter than A E since the electro-motive foi'ce at S is 

 necessarily less than at A, the electro-motive force diminishing 

 gradually from A to B. Similarily A E Fig. 4 representing tlie 

 electro-motive force at A Fig 1, let A T B represent the resistance 

 offered by A X R B Fig. 1 to the passage of the current. The line 

 A T B Fig. 4 being shorter than the line A S B, the resistance being 



greater, the elec- 

 tro-motive force 

 will be diminished 

 more suddenly and 

 the point T where 

 the current from T 

 Fig. 1 passes into 

 ^ the galvanometer 

 will consequently 

 be nearer A, and T G Fig. 

 4, will then represent the 

 electro-motive force at that 

 point and being equal to the 

 electro-motive force at S Fig. 

 3 it must be equal to S G. 

 But if S G be equal to T G, 

 which must necessarily be 

 the case since they represent 

 the electro-motive forces through whose equal and opposed effects 

 the galvanometer needle remains at zero, it follows that A T : T B 

 : : A S : S B or what is the same thing that X : R : : A S : S B (1). 

 Substituting in (1) the values of R, A S, S B as experimentally 

 determined and we obtain X : 100 : : 500 : 500 or X = 100 ohms. 

 That is to say that X the nerve or muscle offers a resistance to the 

 passage of an electrical current that is equal to 100 ohms. In deter- 



FiG. 3. 



