and on the Theory of Magnetism. 83 



midway between the two, or they are not of equal power, it goes 

 alowly towards one of them, and acts with it just as with the 

 single wire of the last paragraph. 



Fig. 11 and 12 exhibit more distinctly tbe direction of the 

 forces which influence the poles in passing between two dissi- 

 milar wires : fig. 1 1 , when the i)ole draws up between tlie wires ; 

 fig. 12, the pole thrown out from between them. The poles and 

 state of the wire are not marked, because the diagrams illus- 

 trate the attraction and repulsion of both poles : for any parti- 

 cular pole, the connexion of the wires must be accordingly. 



If one of the poles be brought purposely near either wire 

 in the position in which it appears to attract most strongly, still 

 if freedom of motion be given by a little tapping, the needle 

 will slip along till it stands midway across the wire. 



A beautiful little apparatus has been made by M. de la 

 Rive, to whom I am indebted for one of them, consisting of a 

 small voltaic combination floating by a cork ; the ends of the 

 little zinc and copper slips come through the cork, and are 

 connected above by a piece of silked wire which has been 

 wrapped four or five times round a cylinder, and the wires tied 

 together with a silk thread so as to form a close helix about one 

 inch in diameter. When placed on acidulated water it is very 

 obedient to the magnet, and serves admirably to transform, as 

 it were, the experiments with straight wires that have been 

 mentioned, to the similar ones made with helices. Thus, if a 

 magnet be brought near it and level with its axis, the apparatus 

 will recede or turn round until that side of the curve next to 

 the nearest pole is the side attracted by it. It will then approach 

 the pole, pass it, recede from it until it gains the middle of the 

 magnet, where it will rest like an equator round it, its motions 

 and position being still the same as those before pointed out. 

 (Fig. 13.) If brought near either pole it will still return to the 

 centre ; and if purposely placed in the opposite direction at the 

 centre of the magnet, it will pass oil' by either pole to which 

 it happens to be nearest, being apparently first attracted by 

 the pole and afterwards repelled, as is actually the case; will, 

 if any circumstance disturbs its perpendicularity to the magnet, 

 G 2 



