PLUCKER ON THE RELATION OF MAGNETISM, ETC. 377 



netically excited between the poles of a magnet. However, 

 every idea of the tenability of the view in question must neces- 

 sarily be given up in consequence of the experiment which I 

 shall next detail. 



4. Even in my earliest experiments on the magnetic or dia- 

 magnetic state of different vegetable and animal structures, in 

 which especially very small masses were examined with the 

 neai'est possible proximity of the poles, I often found what ap- 

 peared to me as anomalies, that these bodies, although placed so 

 near one of the poles as to touch it, were repelled by it, yet they 

 arranged themselves between the poles like a magnetic body. 

 The wings of the cockchafer especially, which arranged them- 

 selves magnetically between the poles, i. e. with their longitu- 

 dinal direction from one pole to the other, when placed with their 

 broad surfaces next one of the poles, were decidedly repelled by 

 it, like a diamagnetic body. This was an anomaly the explana- 

 tion of which I reserved for future experiments, because at this 

 time the experiments on the action of the poles of the magnet 

 upon the optic axes had temporarily engaged my whole atten- 

 tion. These experiments, to which the former treatise has been 

 devoted, were originated by the inquiry, as to what was the 

 cause of the magnetism of certain vegetable structures, and 

 whether the direction of the fibres did not perhaps exert some 

 influence upon the position which vegetable stx'uctures assumed 

 when suspended by a silkworm thread between the poles of a 

 magnet. On resuming this question, I placed the barks of 

 several trees, all of which were magnetic, so as to oscillate ; and 

 on doing so, especially with a piece of the bark of the cherry- 

 tree of a rectangular form, about 15 millim. long and half this 

 breadth, I obtained the unexpected result, that when this was 

 suspended so that whilst its longitudinal direction oscillated 

 horizontally between the two apices of the poles, which were 

 approximated as much as possible, it could still move freely, it 

 placed itself equatorially like a diamagnetic body ; but when the 

 poles were removed further apart, or when the bark was raised 

 above or lowered below the line of the poles, it became axial, 

 like a magnetic body. It is evident that in this experiment, 

 which I repeated with different pieces of cherry-tree bark of dif- 

 ferent sizes and with the fibres variously arranged, there were 

 two distinct forces in a constant state of activity, and that one, 

 the magnetic, diminished less in proportion to the inci-euse of the 

 distance than the other, the diamagnetic. 



