ANIMAL ELKCTRICITV. — LKCTURK !!. 39 



I will take r small and R large, so as to take R 

 as a sufficiently accurate denominator of the fraction 

 iT^j^. Taking R at, say, 100,000 ohms., and r 

 successively at i, 2, 3, 4 ohms, you see that the 

 deflections are i, 2, 3, 4, i.e., current varies directly 

 as pressure. Taking r at, say, 4 ohms, and R at 

 100,000, 200,000, 300,000, 400,000, the deflections 

 are 4, 2, i^, i, i.e., as i, \, \, \, i.e., current varies 

 inversely as resistance, which you may recognise as 

 an instance of the fundamental principle known as 

 Ohm's Law. 



Fig. 12. — Records of deflections by the dead-beat and by the ordinary 

 (partially damped) galvanometer. 



The time-records are in quarter-minutes; the "falling time" of the dead- 

 beat magnet is about 15 seconds; the partially-damped magnet has 7 com- 

 plete oscillations in I minute, i.e., an oscillation period of %\ seconds. 



In the galvanometer now at work before you the 

 movements of the magnet are partially damped ; you 

 see that at each deflection the spot swings to and fro, 

 above and below its position of rest, by a series of 

 diminishing oscillations. Many of the records you 



