Bodies are repelled frum the Pules of a Magnet. 273 



made use of in experiments on diamagnetism^ but the dimensions 

 stated do not mark the practical limit of the size of the bar. A 

 solid bismuth cylinder, 14 inches long and 1 inch in diameter, 

 was suspended in a helix 5*7 inches long, 1'8 inch internal dia- 

 meter, 4 inches external diameter, and composed of copper wire 

 O'l of an inch in thickness : when a current of twenty cells was 

 sent through the helix, and the magnets (only two of them were 

 used) were excited by one cell, all the pheenomena exhibited by 

 figs. 40, 41, 43 and 43, were distinctly exhibited. 



A considerable difference is always necessary between the 

 strength of the current passing through the helix and that which 

 excites the cores, so as to prevent the induction of the cores, 

 which of itself would be followed by repulsion, from neutralizing, 

 or perhaps inverting, the induction of the helix. When two 

 magnets were used and the helix was excited by ten cells, I found 

 the magnetic excitement by one or two cells to be most advan- 

 tageous ; when the cores were excited by ten. or even five cells, 

 the action was always repulsive*. When four magnets were 

 applied and the helix was excited by a battei'y of ten or fifteen 

 cells, a power of five cells for the magnets was found efficient. 



The deportment of paramagnetic bodies is so well known, that 

 it might be left to the reader to discern that in all the cases 

 described it is perfectly antithetical to that of the diamagnetic 

 bod3\ I have nevertheless thought it worth while to make the 

 corresponding experiments with an iron bar; to facilitate com- 

 parison, the results are placed side by side in Plate IV. with those 

 obtained with the bar of bismuth. It must be left to the reader 

 to decide whetiier throughout this inquiry the path of strict in- 

 ductive reasoning has been adhered to : if this be the case, then 

 the inference appears unavoidable, that the dianiagnetic force 

 is a polar force, the polarity of diamagnetic bodies being opposed 

 to that of paramagnetic ones under the same conditions of ejccite- 

 mentf. 



* The perfect similarity of this deportment to that of soft iron under the 

 same circum stances is evident. 



t I would gladly refer to M. Pluckei's results in connexion with this sub- 

 ject had I been suecessl'ul in oi)taininj; them ; I will here, however, intro- 

 duce the description of his most decisive experiment in his own words. 

 (See Scientific Memoirs, New Ser. p. o.S6.) 



" From considerations of which we shall speak afterwards, it appeared 

 to ine probable that bismuth not only assumes polarity in the vicinity of a 

 matfnetie ])ole, but that it also retains the polarity for some time after the 

 excitation has taken place; or, in other words, that bismuth retains a ])or- 

 tiou oi' its ma}i;uetism permanently, as steel, unlike soft iron, retains a portion 

 of the magnetism excited In it by induction. My conjcctiu'e has been cor- 

 roborated by experiment. 



" I liuii}^ a bar of bismuth, 15 millims Ions'; and .5 millims. thick, between 

 the pointed jjoIcs of tlie large electro-niagiiet ; it was suspeiuled horizon- 



