PLUCKER ON DIAMAGNETIC POLARITY. 581 



pole and the line of its south pole to the south pole of the 

 magnet. When this was communicated to me in a friendly 

 manner, I immediately repeated the experiment with a single 

 pole of the magnet only, and showed the polarity of the bar of 

 bismuth alluded to in PoggendorfF's Annalen for March, p. 475 ; 

 and this not only on the side turned towards the exciting pole, but 

 also on that turned from it, by the attraction and repulsion in 

 the ordinary manner. Except that I principally used for this 

 purpose a soft iron bar, and that pole of the magnet which acted 

 diamagnetically upon the bismuth ; I also gave it, according to 

 the position in which it was kept, the polarity required in each 

 instance. 



5. Although the above experiments show indisputably that 

 diamagnetism consists in a polar excitation, still there are great 

 difficulties to be overcome before this theory can be considered 

 as generally established. These long appeared to me so great, 

 that I completely laid them aside, and did not again resume 

 them until the polarity had been so decidedly proved. In fact, 

 I think, after a superficial mathematical consideration, that 

 the repulsion of the optic axes of crystals by the magnet, which 

 I was the first to observe, and the preponderance of this repul- 

 sion, when the poles are a great distance apart, over the mag- 

 netic or diamagnetic action upon their substance, might be very 

 easily explained by a supplemental assumption ; but the facts 

 described in my second memoir appear to me inexplicable even 

 at the present time. When a piece of wood-charcoal (merely in 

 consequence of its form, and as the longitudinal direction may 

 be taken as either in or against the direction of the fibres, 

 quite independently of its structure) in close proximity to the 

 poles assumes an equatorial position and at a great distance an 

 axial position, this is expressed in the language of theory as 

 follows : — The poles of the magnet excite in the charcoal Am- 

 pere's molecular currents, which, when the poles are approxi- 

 mated, perhaps run from east to west ; when the poles are sepa- 

 rated, run from west to east. 



6. According to the experiment last detailed, it cannot be 

 doubted that as the distance of the two poles apart is increased 

 the molecular currents in the charcoal (at least the resulting 

 ones) reverse their direction, because they first produce diamag- 

 netism and then magnetism : we are therefore compelled to 

 admit that the same pole of the magnet, according to the dif- 



