and on the Theory o/" Magnetism. 91 



It has been stated that the poles circulate in opposite direc- 

 tions round the wires, and they would consequently circulate 

 in opposite directions through and round the helix ; when, 

 therefore, one end of the helix was near that pole, which 

 would, according to the law stated, enter it and endeavour to 

 go through, it would enter, and it would continue its course 

 until the other pole, at first at a distance, would be brought 

 within action of the helix ; and, when they were both equally 

 within the helix and consequently equally acted on, their 

 tendency to go in different directions would counterbalance 

 each other, and the needle would remain motionless. If it 

 were possible to separate the two poles from each other, they 

 would dart out of each end of the helix, being apparently 

 repelled by those parts that before seemed to attract them, as 

 is evident from the first and many other experiments. 



By reversing the needle and placing it purposely in the helix 

 in that position, the poles of the needle and the corresponding 

 poles of the helix as they attract on the outside, are brought 

 together on the inside, but both pairs now seem to repel ; and, 

 whichever end of the helix the needle happens to be nearest 

 to, it will be thrown out at. This motion may be seen to exhibit 

 in its passing state, attraction between similar poles, since the 

 inner and active pole is drawn towards that end on the inside, 

 by which it is thrown off on the outside *. 



These experiments may be made with the single curve of 

 M. de la Rive, in which case it is the wire that moves and 

 not the magnet, but as the motions are reciprocal, they may 

 be readily anticipated. 



A plate of copper was bent nearly into a cylinder, and its 

 edges made to dip into two portions of mercury ; when placed 

 in a current it acted exactly as a helix. 



A solid cylinder of silked wire was made exactly in fashion 

 like a helix, but that one length of the wire served as the 

 axis, and the folds were repeated over and over again. This 



* The magnetizing power of the helix is so strong that if the cxpciiinont 

 be made slowly the needle will have its magnetism changed, and thi? 

 result will be fallacious. 



