226 Prof. Dove on the Induced Currents excited 



closed wire, efg h, or perpendicular to its plane an iron bar s», 

 then this equilibrium of the currents will be destroyed. In 

 the first case the current in « /3 will be retarded by the current 

 induced in ej'gh, and consequently its galvanometric action 

 remains unchanged, but its property of produced physiologi- 

 cal effects and of magnetizing steel will be diminished. The 

 magnetism o( s n, which vanished on the cessation of the cur- 

 rent In abed, will increase the quantity of electricity circu- 

 lating in a/3, and consequently the action of the current will 

 be increased. 



If we suppose this electro-magnetized iron, 5?^, surrounded 

 by a conducting wire, on account of the magnetism disappear- 

 ing in s n, a greater quantity of electricity will be set in motion 

 in a/3 than in yS, but on account of the simultaneously ex 

 cited current in ej'gh this electricity will be moved with less 

 rapidity than the smaller quantity in y 5. 



Three different cases may here occur: — 



1st. The increased quantity of electricity raises any one 

 particular action of the current more than the simultaneous 

 retarding of the current decreases it. 



2nd. The action which is increased by the greater quantity 

 of electricity is exactly compensated for by the retarding of 

 the current. 



3rd. The retarding of the current weakens any particular 

 action more than it is strengthened by the increased quantity 

 of electricity. 



In all experiments which have as yet been made respecting 

 induction, the first case alone has been observed. The fol- 

 lowing experiments show that the other two cases can occur, 

 and indeed for one particular action of the current u /3, the one 

 case, and for another the third. 



A bundle of isolated iron wires does not admit of the for- 

 mation of electrical streams circulating round the whole bun- 

 dle; iti however, we inclose it in a conducting case or covering, 

 as for instance in a brass tube, the bundle then represents the 

 magnet sw, and the covering of the bundle the wire ej'gh: 

 in the case of a massive bar of iron, its surface may be. con- 

 sidered as the inclosing case ejgh. S71 witii its surrounding 

 wire eJgh is therefore such an electro-magnet. 



In order to increase the action a b and c d are cylindrical 

 spirals, « /3 and y 8 are larger spirals which fit over a b and c d\ 

 they are separated from each other by a tube of pasteboard, 

 and all the spirals are covered with silk and carefully var- 

 nished. The bars of iron and bundles of wires are inserted 

 into the spiral a b. 



1. If the primary current abed is that of a galvanic bat- 



I 



