GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 45 



Suppose that the resistance of the galvanometer circuit (R') be 

 only 10 ohms, and suppose we remove from the rheostat the plug 

 that represented 0.1 ohm resistance, then one-hundredth of the 

 current will pass through the galvanometer. If we make the resist- 

 ance in the short circuit 0.2 ohm, then one-fiftieth of the current 

 will flow through the long circuit. 



Problem. In this way we may increase the galvanometer current 

 step by step until the maximum is reached. 



What is the maximum current to be derived when the resistance 

 in the galvanometer circuit (R') equals 10 ohms, the maximum 

 resistance of the rheostat (R) equals 100 ohms, external resistance 

 in circuit between cell and rheostat (r) equals 1 ohm, E.M.F.= 

 1 volt, and internal resistance of cell 4 ohms? 



(b) The Simple Rheocord. 



Besides the methods already used for varying the strength of the 

 current one may use the derived current. 



The simple rheocord (Fig. 25) may be used for this purpose. 



FIG. 25 



Rheocord with contact key. 



1. Appliances. One or more cells; simple rheocord; five wires; 

 galvanometer.- 



2. Experiments and Observations. (1) Set up the apparatus 

 as shown in Fig. 25. From the figure we see that from the cell 

 to post A, thence through the German-silver wire to post B and 

 back to the cell makes a complete circuit. Having reached the 



