248 FRA OMENT8 OF SCIENCE. 



a current through the helices, and observing that the 

 magnets swung perfectly free, it was first arranged that the 

 bismuth cylinders within the helices had their central or 

 neutral points opposite to the poles of the magnets. All 

 being at rest the number on the scale marked by the cross 

 wire of the telescope was 572. The cylinders were then 

 moved, one up, the other down, so that two of their ends 

 were brought to bear simultaneously upon the magnetic 

 poles: the magnet moved promptly, and after some oscil- 

 lations* came to rest at the number 612; thus moving 

 from a smaller to a larger number. The other two ends of 

 the bars were next brought to bear upon the magnet: a 

 prompt deflection was the consequence, and the final 

 position of equilibrium was 526: the movement being 

 from a larger to a smaller number. We thus observe 

 a manifest polar action of the bismuth cylinders upon 

 the magnet; one pair of ends deflecting it in one direc- 

 tion, and the other pair deflecting it in the opposite 

 direction. 



Substituting for the cylinders of bismuth thin cylinders 

 of iron, of magnetic slate, of sulphate of iron, carbonate of 

 iron, protochloride of iron, red ferrocyanide of potassium, 

 and other magnetic bodies, it was found that when the 

 position of the magnetic cylinders was the same as that of 

 the cylinders of bismuth, the deflection produced by the 

 former was always opposed in direction to that produced by 

 the latter; and hence the disposition of the force in the 

 diarnagnetic body must have been precisely antithetical to 

 its disposition in the magnetic ones. 



But it will be urged, and indeed has been urged against 

 this inference, that the deflection produced by the bismuth 

 cylinders may be due to induced currents excited in the 

 metal by its motion within the helices. In reply to this 

 objection, it may be stated, in the first place, that the deflec- 

 tion is permanent, and cannot therefore be due to induced 

 currents, which are only of momentary duration. It has 

 also been urged that such experiments ought to be made 

 with other metals, and with better conductors than bismuth; 

 for if due to currents of induction, the better the conductor 

 the more exalted will be the effect. This requirement was 

 complied with. 



* To lessen these a copper damper was made use of. 



