LAW OF PULSATIONS. 



133 



is inserted in one branch, and that the resistance of the 

 other branch is altered, then the strength of the cur- 

 rent passing through the nerve will change, although 

 the conductor which contains the nerve remains un- 

 altered ; the current within the nerve will increase 

 in strenofth when the resistance in the other branch is 

 increased, and it will decrease when the resistance in 

 this branch is decreased. 



The resistance of a wire being j)roportionate to its 

 length, it is only necessary to arrange, as the conductor 



Fig. 32. EiiEociionD. 



A S, a wire the length of which can be in some way 

 altered. The simplest way of doing this is by extend- 

 ing the wire in a straight line and moving a sliding- 

 piece along it, so that any required length of the wire 

 may be brought into the conductor. Such an apparatus 

 is called a rheochord, from pFos, a current, and x^P^V^ 

 a chord — because the current is conducted along a wire 

 extended like a chord. A rheochord of the simplest kind 

 is represented in fig. 32. The current of the chain 

 P Z traverses the wire A B, From A a branch con- 



