284 M. A. F. Sundell on Galvanic Induction. 



the inducing-force. It was for the purpose of verifying this 

 formula that the experiments described in this paper were made, 

 in the physical laboratory of the Royal Academy of Sciences, 

 Stockholm. 



1. The induction-coils were arranged in the following manner. 

 A copper wire., 0*5 millim. thick, insulated with silk, was wound 

 in the rectangular incision on the circumference of a circular 

 wooden plate. Four such coils were used. Two of the plates 

 had a diameter of 44*4 centims. ; the breadth of the incision 

 was 09 centim., and its depth 0*55 centim. • thus the radius 

 of the plate, from its centre to the bottom of the incision, was 

 21*65 centims. The spirals of these two coils were arranged in 

 two sets. The other two plates had a radius of 6*95 centims. 

 to the bottom of the incision, the breadth of which was 0*6 

 centim., and the depth 0"3. The incisions of these two plates 

 were wholly filled up by the wire spirals. In the centres of 

 the plates round holes were drilled ; thus the plates could be 

 placed on a prismatic wooden bar, on one side of which a paper 

 scale of centimetres was extended. The primary coil was fixed 

 on the end of the bar ; the secondary coil was movable along it. 

 In every experiment the plates were placed with their plane 

 perpendicular to the length of the bar; thus its geometrical 

 axis passed through the centre of the coil perpendicular to the 

 planes of its spirals. 



The primary current was produced by a galvanic battery of 

 four to six Bunsen's cells. The intensity of this current was 

 measured by a tangent-galvanometer. The disjunctor^ or the 

 apparatus for effecting the induction, consisted of two wheels of 

 boxwood on a common axis with a handle. The peripheries of 

 the wheels were divided, by means of sixteen brass plates, into 

 intervals alternately conducting and non-conducting. Two 

 brass springs of equal length pressed on each periphery. The 

 one pair of springs made part of the primary circuit. Thus, by 

 turning the handle, the primary current was alternately esta- 

 blished and destroyed ; at the moment of its breaking, the other 

 pair of springs was in contact with a brass plate of the second 

 wheel, thus completing the secondary circuit, in which a Weber's 

 magnetometer was inserted. But when the first pair of springs 

 just touched a brass plate, then the second pair pressed on a 

 non-conducting interval, and the secondary circuit was incom- 

 plete. By this arrangement we got only secondary currents of 

 the same direction, viz. those produced by breaking the primary 

 current. 



In the experiments the handle of the disjunctor was turned 

 once round in half a second, sixteen secondary currents being 

 thus produced. At every complete turn a brass spring pressed 



