38 



ANIMAL ELECTRICITY. LECTURE II. 



We shall therefore neglect compensation, and if 

 the nerve current is so large as to send the spot " off 

 scale" or ''off plate," readjust the deflection by means 

 of a controlling magnet such as that fixed above the 

 case of Thomson (Kelvin) galvanometers. 



We shall have yet another use to make of the re~ 

 sistances r R when we come to study the polarisa- 

 tion increment. We shall then require to deliver to 

 the nerve, pressures of, say, o"i, 0*2, 0*3, &c., volt, and 

 shall do this without altering the connections, by ad- 

 justment 'of the resistances. 



I will illustrate the use of these resistances, and at 

 the same time give an example of the principle that 

 deflection (by current) varies directly as pressure, and 

 inversely as resistance, by the following pair of 

 experiments. This is the circuit (fig. 11); it need 



V5L 



Fig. II. — A Compensator. 



not be separately put up ; it is sufficient to close the 

 superfluous keys K, and K^ of the circuit as given in 

 fig. 10, leaving only K3 and K^ open. 



