198 



Mr. W. Sturgeon 07i Electro- Ma"ncts. 



the magnetic poles in the extremities of the bar will at all 

 times be determined by the direction of the electric stream, 

 and that no vicissitude can possibly take place in the one 

 without a corresponding and simultaneous vicissitude in the 

 character of the other, — it follows that the revolving wire will 

 uniformly proceed in one and the same direction, whatever 

 may be the nature of the electric stream ; and that no vicissi- 

 tudes in the direction of motion can possibly be accomplished 

 by any similar arrangement. 



Now, as the direction in which the wire revolves will be de- 

 termined by the direction in which the spirals encompass the 

 iron, it is plain that the apparatus may be so constructed as 

 to perform its revolutions in any direction the experimenter 

 may think proper to select : but the selection once made, and 

 the* standard spiral determined on, the apparatus becomes in- 

 capable of exhibiting that beautiful diversity of revolving mo- 

 tions which proceed from various combinations of the electric 

 and magnetic forces. 



If, however, the electric current were not to be continuous 

 from one of the extreme cups to the other, the apparatus 

 might then be made to perform the usual variety of electro- 

 magnetic rotations; because in that case one current might 

 be employed to give polarity to the iron, whilst another could 

 be transmitted in any required direction through the pendent 

 revolving wire. 



Upon the same principle a bar of soft iron, properly 

 connected, will rotate on its axis with an 

 astonishing velocity ; the direction of mo- ''»• • 

 tion being always determined by the cha- jx 



racter of the helical conductor. The appa- 

 ratus which I use for the exhibition of this 

 interesting phtBnomenon is similar to that 

 by means of which I showed the rotation 

 of a steel magnetic bar on its axis, by 

 the influence of two electric currents 

 (Phil. Mag. vol. Ixiv. p. 246) ; the transient 

 electro-magnet in this case being substi- 

 tuted for the permanent steel magnet in the 

 other experiment. The manner in which 

 the spiral is airanged will be understood 

 by contemplating fig. 2. The ends of the 

 spiral are soldered to the cylindrical bar of 

 iron at the points a a, and to the centre is 

 soldered a short wire with a descending 

 point for the purpose of maintaining an 

 uninterrupted connection with an annular mass of mercury in 



which 



