supposed Polarity of Diamagnetic Bodies. 103 



together, will show the phenomena of revulsion very well ; 

 and that according to the direction of the leaves, and not of 

 the external form. Gold, silver, tin and copper have the re- 

 vulsive effects thus greatly exalted. Antimony, as I have 

 already shown, exhibits the effect well (2514. 2519.). Both 

 it and bismuth can be made to give evidence of the induced 

 currents produced in them when they are used in thin plates, 

 either single or associated, although, to avoid the influence of 

 the diamagnetic force, a little attention is required to the 

 moments of making and breaking contact between the voltaic 

 battery and the electro- magnet. 



2687. Copper, when thus divided into plates, had its revul- 

 sive phenomena raised to a degree that I had not before ob- 

 served. A piece of copper foil was annealed and tarnished 

 by heat, and then folded up into a small square block, half an 

 inch in the side and a quarter of an inch thick, containing 

 seventy-two folds of the metal. This block was suspended by 

 a silk film as before (2248.), and whilst at an angle of 30° or 

 thereabouts with the equatorial line (2252.), the electro-magnet 

 was excited ; it immediately advanced or turned until the 

 angle was about 45° or 50°, and then stood still. Upon the 

 interruption of the electric current at the magnet the revulsion 

 came on very strongly, and the block turned back again, 

 passed the equatorial line, and proceeded on until it formed 

 an angle of 50° or 60° on the other side ; but instead of con- 

 tinuing to revolve in that direction as before (2315.), it then 

 returned on its course, again passed the equatorial line, and 

 almost reached the axial position before it stood still. In fact, 

 as a mass, it vibrated to and fro about the equatorial line. 



2688. This however is a simple result of the principles of 

 action formerly developed (2329. 2336.). The revulsion is 

 due to the production of induced currents in the suspended 

 mass during the falling of the magnetism of the electro- 

 magnet ; and the effect of the action is to bring the axis of 

 these induced currents parallel to the axis of force in the mag- 

 netic field. Consequently, if the time of the fall of magnetic 

 force, and therefore of the currents dependent thereon, be 

 greater than the time occupied by the revulsion of the copper 

 block as far as the equatorial line, any further motion of it 

 by momentum will be counteracted by a contrary force ; and 

 if this force be strong enough the block will return. The 

 conducting power of the copper and its division into laminae, 

 tend to set up these currents very readily and with extra 

 power ; and the very power which they possess tends to make 

 the time of a vibration so short, that two or even three vibra- 

 tions can occur before the force of the electro-magnet has 



