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Article XIII. 



On the Theory of Diamagnetism, the Explanation of the 

 transition from the Magnetic to the Diamagnetic deportment, 

 and the Mathematical treatment of the Phenomena observed 

 in Crystals, By M. Plucker, Professor of Natural Phi- 

 losophy in the University of Bonn. 



[From PoggendorfF's Annalen, Ixxxvi. 1.] 



In December 1849, 1 handed over to the Society of Sciences at 

 Haarlem, a memoir, the last part of which, treating as it did of 

 the magnetism of crystals with the addition of some further 

 mathematical developments, and the omission of some experi- 

 ments, was immediately edited in French. These investigations, 

 determined by the official dates and intended for the press, 

 have remained up to the present time unprinted. This circum- 

 stance has placed me in a false position with regard to the 

 investigations published on the same subject by MM. Kno- 

 blauch and Tyndall. Reluctantly, and with some dissatisfaction, 

 I once more lift my pen to communicate the following literal 

 extracts from the original memoir at present before me. 



Part I. 



11. It is a known fact that a spiral, through which a gal- 

 vanic current is suffered to pass, converts a bar of iron placed 

 within it into a magnet. A bar of bismuth under the same 

 circumstances w ill also become a magnet, but its poles are those 

 of the iron reversed. 



To prove this by experiment, I took two equal hollow spirals 

 120 miUims. long, having an interior diameter of 26 millims. 

 and an exterior diameter of 52 millims. (Plate V. fig. 3). The 

 copper used in their construction was 5 miUims. in diameter. 

 Both spirals w^re placed at right angles one above the other, 

 and in the lower one a bar of iron 130 millims. long and 

 21 millims. thick was placed, while in the upper spiral a bar of 

 bismuth 80 millims. long and 15 millims. thick, was introduced 

 and suspended vertically from the arm of a fine balance. It 

 was so equilibrated by a scale-pan suspended from the opposite 

 arm, and into which fine shot was placed, that the two cy- 



