162 Proj, Tyndall, on the Disposition of Force [Feb. 1, 



brought forward was conducted. It is manifest that if a second 

 helix be placed between the poles S N with a cylinder within it, the 

 action upon the astatic magnet may be exalted. This was the 

 arrangement made use of in the actual inquiry. Thus to intensify 

 the feeble action, which it is here our object to seek, we have in the 

 first place neutralized the action of the earth upon the magnets, by 

 placing them astatically. Secondly, by making use of two cylinders, 

 and permitting them to act simultaneously on the four poles of the 

 magnets, we have rendered the deflecting force four times what 

 it would be, supposing only a single pole to be used. Finally, 

 the wliole apparatus was enclosed in a suitable case, which protected 

 the magnets from atmospheric currents, and the deflections were 

 read ott' through a glass plate in the case, by means of a telescope 

 and scale placed at a considerable distance from the instrument. 



A pair of bismuth cylinders was first examined. Sending a 

 current through the helices, and observing that the magnets swung 

 perfectly free, it was first arranged that the cylinders within the 

 helices had their central 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 so that 

 two ends were brought to bear simultaneously upon the magnetic 

 poles : the magnet moved promptly, and after some oscillations* 

 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 direction, 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, proto- 

 chloride 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 diamagnetic 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 is 

 purely due to the currents of induction excited in the mass by its 

 motion within the helices. In reply to this objection, it may be 

 stated, in the first place, that the deflection 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 



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



