750 PLUCKER ON THE DETERMINATION OF THE 



are perfectly explained by the fact that the electro-magnet acts 

 throughout upon a combination of magnetic and diamagnetic 

 substances, and by the magnetism diminishing less in propor- 

 tion than the diamagnetism with the force of the electro-mag- 

 net, and thus also with the distance from it. This is in fact 

 what I had previously stated, even in the first of the two above- 

 mentioned memoirs, without being aware of the phaenomena 

 which have been described, in the following words : — " It ap- 

 pears moreover to be a necessary consequence of the results 

 obtained, that the same body, perhaps in the form of a sphere, 

 at a greater or less distance from one of the poles of the magnet, 

 may at one time be repelled throughout its entire mass, at another 

 may be attracted." 



55. Thus if we could increase the power of the electro-magnet 

 to such an extent, that not only the magnetic attraction, but 

 also the diamagnetic repulsion, exceeded the force of gravity, we 

 should have the remarkable phaenomenon, that a body formed 

 from a proper mixture of magnetic and diamagnetic substances, 

 and oscillating freely in the air above the poles of the magnet, 

 would be retained by the latter. The experiment might be per- 

 formed even now, if we were to invert the poles of the magnet, 

 when the force of gravity might be balanced by the magnetic 

 attraction acting in an opposite direction, instead of by the 

 counter weight ; and then the excess of the magnetic attraction 

 alone over the gravity and the diamagnetic repulsion would 

 remain actiAC. 



- 56. That the diamagnetism increases more rapidly than the 

 magnetism when the strength of the electro-magnet increases, 

 may be confirmed by direct weighings. 



To show this provisionally, I took a hollow hemisphere of 

 sheet brass, and suspended it in the same manner as the watch- 

 glass. About 115 grras. of bismuth were then fused in it, and 

 allowed again to cool. The solidified mass could be taken out, 

 and again replaced. On using in succession two, three and ten 

 cells, the attractions of the empty bi'ass cup amounted respect- 

 ively to — 



arm. grm. grra. 



0-69 113 2-15; 



and that of the brass cup containing the bismuth to — 



0-53 071 0-48 ; 



whence we have, as the diamagnetism of the bismuth, 



0-14 0-42 1-67. 



