Rutherford. — On Magnetic Viscosity. 197 



the first 50^00 of a second the curve of rise is nearly a 

 straight hne. 



The curve of rise in the case of short cyhndrical iron rods 

 like the cores of induction-coils resembles very closely curve 

 1, for the inductance is sensibly constant. 



If a closed secondary is wound over the primary the cur- 

 rent rises much more rapidly than when the secondary is 

 open, as we should expect from theory. 



Duration of Induced Currents at Make and Break. 



The time-apparatus could not only be used for determina- 

 tion of times of rise of currents in various circuits, but also for 

 determining the duration of the current in the secondary at 

 make and break. 



'8o,n 



"yiBilhihc £t:'f 



Fig 4 



The method is a very simple oiie, and the duration 

 of the secondary current may be determined under what- 

 ever conditions we please, since the resistance and in- 

 ductance of the galvanometer does not affect the duration 

 of the current in the circuit w'hich is being experimented 

 on. 



One terminal of the battery is connected to F, and when 

 the lever A B is in position the current passes along the lever 

 B A, through the primary P, and through a resistance-box back 

 to the other electrode of the battery. 



The secondary circuit is connected through a resistance- 

 box R and the shunt-lever C D. The ballistic galvanometer is 

 a shunt oli" the lever E D. 



The resistance in the secondary Q E D R may be adjusted 

 to any required value. 



When the falling weight is released, on reaching the lever 

 AB it breaks the primary. The induced current at break 

 commences to circulate in the secondary round the circuit 

 QEDR. 



No appreciable part of the current flows through the 

 galvanometer, as the resistance of the lever C D is extremely 

 low. 



