16 Prof. E. Edlund on the Path of Electrical Induction- and 



weaker ; moreover, of the two opposite induction-currents, equal 

 parts pass through the bridge, by which their action on the needle 

 is annulled. Only that part of the two currents which traverses 

 the spark can affect the needle. In order to make this as small 

 as possible, the resistance in the bridge must be small as com- 

 pared with the sum of the resistance in the rheostat and in the 

 spark. But in proportion as the resistance in the bridge is di- 

 minished, the deflection of the disjunction-current is also dimi- 

 nished ; for this now takes its path more and more through the 

 bridge instead of through the galvanometer. Hence the resist- 

 ance in the bridge must not be made smaller than so that the 

 action of the induction-currents upon the magnetic needle just 

 becomes imperceptible. 



Experiments specially made for this purpose showed that a 

 German-silver wire 27 centims. in length and 0*7 in diameter ful- 

 filled these conditions; audit was therefore used as a bridge in front 

 of the galvanometer. That the action of the induction-currents 

 upon the needle was thus rendered imperceptible was shown as 

 follows : — An induction-coil, C, of exactly the same nature as 

 the galvanometer-coil, was inserted between m and h, and in 

 front of it a German-silver wire as bridge, of the same length and 

 the same diameter as the previous one. The galvanometer-coil 

 and the coil R were thus both in the same position ; they must 

 produce equal induction-currents ; and equal parts of these must 

 traverse the respective bridges. If, then, it can be proved that 

 the induction-currents from the coil C have no influence on the 

 deflection of the magnetic needle when the bridge is in front 

 of this coil, the proof is valid also in the case of the galvano- 

 meter-coil. Of the observations made the following may be 

 adduced, with regard to which it must be observed that the 

 resistance in the conducting-wires and in the spark was so great, 

 compared with that in the coil and in the German- silver wire 

 just mentioned, that the latter need not be taken into account. 



Experiment 1. — The German-silver wire inserted between m 

 and k. When the machine was put in motion the following 

 deflections were observed: — 



35 '5 divisions. 



35-5 „ 

 Mean . . 355 „ 

 Experiment 2. — The coil C was inserted between m and k } so 

 that the German-silver wire formed the bridge : — 



Deflections. 



35-8 



37-6 



Mean . . 36'7 



