PLUCKER ON THE THEORY OF DIAMAGNETI8M. 333 



linders of iron and bismuth were separated by an interval of 

 from 1 to 2 millims. A current from three of Grove's elements 

 could be sent through each spiral in particular and in any re- 

 quired direction ; we will assume the direction to be such that 

 at the upper end of the bar of iron a north pole was excited. 

 In consequence of this the cylinder of bismuth was repelled, 

 but by removing a few grains of shot could be brought into 

 its former position. The current was then conducted through 

 the upper spiral, and first in the same direction as in the lower 

 one; the bismuth cylinder receded again from the iron, but 

 returned to its position as soon as the current was interrupted. 

 When however the direction of the current in the upper spiral 

 was opposed to that below, the cylinder of bismuth was attracted, 

 and did not recede until the current had been intercepted in 

 the upper spiral. The experiment was repeated several times, 

 the action was decided although feeble. The consequences 

 were the same when, through the under spiral, the current was 

 reversed and the upper end of the bar iron thereby converted 

 into a south pole. 



12. With the intention of increasing the effect, the same expe- 

 riment was so modified, that instead of the under spiral the 

 great electro-magnet (Plate V. fig. 4) was made use of. Upon its 

 poles the two heavy semi-armatures were laid, and the round 

 ends brought within a distance of 10 millims. of each other. 

 Then one of the former spirals was so placed upon one of the 

 semi-armatures, that the bismuth cylinders, which moved up 

 and down within it, rested upon the point of the armature when 

 the magnetism was strongest. The magnetism of the great 

 electro-magnet was excited by four of Grove's elements, and 

 then the bismuth cylinder so equilibrated that an interval of 

 2 millims. existed between it and the armature. When the 

 current from five other elements of Grove was transmitted 

 through the spiral in such a direction that an iron bar, substi- 

 tuted for the bismuth, would have a south pole at its end next 

 the armature, which latter was a north pole, then the cylinder 

 of bismuth receded to a height of 4 millims. above the armature, 

 and returned to its former position when the current was in- 

 terrupted. All modifications of the original experiment gave 

 the expected result. 



