supposed Polarity of Diamagnetic Bodies. 107 



pole of the former. If the core be iron, as it approaches the 

 magnet it causes a strong convergence and concentration of 

 the lines of magnetic force upon itself; and these, as they so 

 converge, passing through the helix and across its convolu- 

 tions, are competent to produce the currents in it which are 

 obtained (2653. 2668.). As the iron retreats these lines of 

 force diverge, and again crossing the line of the wire in the 

 helix in a contrary direction to their former course, produce a 

 contrary current. It does not seem necessary, in viewing the 

 action of the iron core, to suppose any direct action of it on 

 the helix, or any other action than this which it exerts upon 

 the lines of force of the magnet. In such a case its action 

 upon the helix would be indirect. 



2697. Then, by all parity of reasoning, when a copper core 

 enters the helix its action upon it should be indirect also. For 

 the currents which are produced in it are caused by the direct 

 influence of the magnet, and must react equivalently upon it. 

 This they do, and because of their direction and known action, 

 they will cause the lines of force of the magnet to diverge. As 

 the core diminishes in its velocity of motion, or comes to rest, 

 the currents in it will cease, and then the lines of force will 

 converge ; and this divergence and convergence, or passage in 

 two directions across the wire of the experimental helix, is 

 sufficient to produce the two currents which are obtained in 

 the advance of the core towards the dominant magnet (2671. 

 2673.). A corresponding effect in the contrary direction is 

 produced by the retreat of the core. 



2698. On the idea that the actions of the core were not of 

 this kind, but more directly upon the helix, I interposed sub- 

 stances between the core and the helix during the times of the 

 experiment. A thick copper cylinder 2*2 inches long, 0*7 of 

 an inch external diameter, and 0*1 of an inch internal dia- 

 meter, and consequently 0*3 of an inch thick in the sides, was 

 placed in the experimental helix, and an iron wire core (2668.) 

 used in the apparatus. Still, whatever the form of the expe- 

 riment, the kind and amount of effect produced was the same 

 as if the copper were away, and either glass or air in its place. 

 When the dominant magnet was removed and the wire core 

 made a magnet, the same results were produced. 



2699. Another copper lining, being a cylinder 2*5 inches 

 long, 1 inch in external diameter, and one-eighth of an inch 

 in thickness, was placed in the experimental helix, and cores 

 of silver and copper five-eighths of an inch in thickness, em- 

 ployed as before, with the best condition of the commutator 

 (2675.) : the effects, with and without the copper, or with and 

 without the glass, were absolutely the same (2698.). 



