580 PLUCKER ON DIAMAGNETIC POLARITY. 



above the enclosed iron bar, on exciting the magnetism by four 

 feebly charged Grove's cells, assumed a very decided equatorial 

 position, and when moved from the equatoi'ial position made 90 

 oscillations during the space of half a minute. After opening 

 the circuit, the pieces of brass and the iron bar were removed 

 without disturbing the two halves of the keeper. The bar of 

 bismuth then also assumed a decided equatorial position, making 

 however only 36 oscillations during the space of half a minute. 

 Hence the directive force of the bar of bismuth had increased 

 by the addition of the equatorial bar of iron in the proportion of 

 36^ to 90^, or of 



1 to 6-25 ; 



thus more than sixfold. 



3. When a hardened bar of steel a little thicker was used 

 instead of the bar of soft iron, the corresponding numbers of the 

 oscillations were 78 and 34. Hence the directive force had be- 

 come increased by the steel bar in the proportion of 



1 to 5-26. 



4. I shall limit myself here to the communication of a single 

 observation, and merely add a few words upon what gave rise 

 to it. 



Faraday's explanation of diamagnetic phaenoraena is so evi- 

 dent, that it M'ould have occurred to every philosopher. In my 

 lectures last summer I expressed it in the following words : — 

 "In bismuth every north pole of a magnet induces a north pole, 

 each south pole a south pole." Diamagnetic polarity is a neces- 

 sary consequence of this explanation. I then tried in vain to 

 detect this polarity. Among other things, I caused a small bar 

 of bismuth to oscillate between the ends of the poles of the cy- 

 linders, inserting however in the two perforated appendages of 

 the poles, instead of the cylinder of iron pointed in front, a 

 similar one made of bismuth ; but on superficial examination I 

 did not observe that any change was produced by the cylinder 

 of bismuth. The results obtained by Reich and Weber induced 

 me again to take up my former experiments ; and this was the 

 origin of the observation described above. It appears to confirm 

 (at least it was instituted with a view to this point) what the ex- 

 periments of Poggendorff have already directly proved, viz. that 

 a bar of bismuth in the equatorial position is a real transversal 

 magnet, which turns the line of its north pole to the north 



