Prof. G. Wiedemann's Magnetic Researches. 55 



clamp by long wires, placed as axially as possible, which ran 

 at first in the direction of the axis of the wire, then coming 

 together in a wide arc, were wound round each other and 

 carried to the poles of the battery. The deviations of the mag- 

 netic mirror were read off upon a scale at a distance of 1 metre. 

 In order to determine the intensity of the current as well as the 

 temporary moments of the wires, a wire ring (Plate I. fig. 1) 

 of 7 centim. diameter was placed in front of the mirror and co- 

 axial with it, cut through at the bottom, and capable of vertical 

 rotation about a horizontal axle of brass, attached to it at its 

 lowest point. The two halves of the axle were provided with 

 copper disks dipping into mercury-troughs. A brass wire 

 was first of all stretched in the torsion-apparatus, the current 

 passed through it and in the proper direction through the 

 wire ring, and this moved axially in front of the steel mirror 

 until the latter showed no deviation, and remained without 

 deviation when the wire was twisted. If, then, the wire 

 ring was turned about its axis into a horizontal position, the 

 deviation of the deflection of the mirror corresponded to the 

 intensity of the current. Employing wires of iron or of nickel, 

 the deflection in the vertical position of the wire ring gave the 

 temporary moment, and in the horizontal position the same 

 increased by a quantity proportional to the intensity of the 

 current. 



Frequently repeated experiments gave decisively the fol- 

 lowing results : — 



If the current passes through an iron wire from the movable 

 clamp to the fixed one, and if the former, as seen in the direc- 

 tion from the movable to the fixed clamp, is rotated in a 

 direction opposite to the hands of a watch, the iron wire 

 acquires a north pole at the fixed clamp, and a south pole 

 with opposite rotation of the clamp. With reversed directions 

 of the current opposite polarities are produced, thus confirm- 

 ing former results. The same takes place after stopping the 

 current. 



But if a nickel wire be employed instead of an iron wire, 

 the results are reversed. If the current passes from the 

 movable to the fixed clamp, and if the former be rotated in a 

 direction opposite to that of the hands of a watch, the wire at 

 the fixed clamp becomes a south pole, and with reversed rota- 

 tion a north pole. Here also the same result is obtained after 

 stopping the current. 



Similar results were obtained also, within certain limits, 

 upon repeated torsion in opposite directions. The deviations 

 of the magnetic mirror far exceeded 50 or 100 scale-divisions, 

 with torsion of + 60° in the case of wires 2 millim. thick, so 



