Soft Iron } especially with weaker decomposing -powers. 49 



Similarly it was proved that the form and other conditions of 

 the secondary turns are without influence. When I caused a 

 thicker wire to run, in 50 wide and irregular turns, round the 

 ring, and formed a secondary closing out of this wire, the oppo- 

 sitely directed division of 50 turns, and the multiplier, I obtained 

 a sensible deflection on reversing the primary current. 



Generally the consecutive induction-impulses are very constant, 

 if only the precaution is taken to turn the commutator several 

 times after each change of the magnetizing-force before com- 

 mencing the observations, as the first deflections are influenced 

 by residual magnetism. 



I pass now to the proper measurements of k and R. 



E 

 As we have seen, it depends upon ascertaining the ratio — of 



the induced electromotive force to the intensity of the inducing 

 current. For this purpose, according to the strength of the 

 latter, various methods were employed. 



"With stronger primary currents, the arrangement shown in 

 fig. 3 (PL III.) was adopted. The current of a galvanic apparatus 

 K (mostly 4-12 Darnell's elements, for more powerful currents 

 12-14 Bunsen) was conducted through two commutators (C, 

 and C 9 ), the primary wire P of the ring, and a circular roll of 

 wire (11) of known dimensions. This roll, intended for the 

 measurement of the primary current, is placed perpendicular to 

 the magnetic meridian, eastward of a magnetometer (M) ; the 

 axis produced of the roll meets the middle point of the magnetic 

 bar. The distance of the latter from the centre of the roll was 

 mostly fixed at 1000 or 1250 millims. 



Moreover the magnet M is now surrounded by a multiplier with 

 close windings. Through this multiplier, provided with a damper, 

 the induced currents are conducted. That is to say, the con- 

 ducting wire of the multiplier is either wound in several turns 

 round the ring, or connected with the above-mentioned divisions 

 of the second layer of wire upon the ring. Lastly, W is a Sie- 

 mens^ resistance-scale, by which the primary current can be, 

 weakened. The observation was effected with scale and telescope. 



The constant current in the roll R imparts to the magneto- 

 meter a certain deviation from the magnetic meridian. By turn- 

 ing the commutator C 1; the current in the primary wire P only 

 is reversed. Thereby an induction-shock is produced in the mul- 



should have been altogether independent of whether a current passed 

 through the turns and in which direction. This., however, was far from being 

 verified when 1 placed the ring close beside the galvanometer — which again 

 intimated the before-mentioned want of homogeneousness. At all events 

 the direct action of the ring upon the galvanometer was quite imperceptible 

 when it held its usual place. 



Phil Mag. S. 4. Vol. 45. No. 297. Tan. 1873. E 



