184 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXIII.) 
I understand the instruction aright, is as follows : a strong horseshoe magnet is laid 
upon a table in such a position that the line joining its two poles is perpendicular to 
the magnetic meridian and to be considered as prolonged on one side ; in that line, 
and near the magnet, is to be placed a small powerful magnetic needle, suspended by 
cocoon silk, and on the other side of it, the pole of a bar magnet, in such a position 
and so near, as exactly to counteract the effect of the horseshoe magnet, and leave 
the needle to point exactly as if both magnets were away. Then a mass of bismuth 
being placed between the poles of the horseshoe magnet is said to react upon the 
small magnet needle, causing its deflection in a particular direction, and this is sup- 
posed to indicate the polarity of the bismuth under the circumstances, as it has no 
such action when the magnets are away. A piece of iron in place of the bismuth 
produces the contrary deflection of the needle. 
2690. I have repeated this experiment most anxiously and carefully, but have never 
obtained the slightest trace of action with the bismuth. I have obtained action with 
the iron ; but in those cases the action was far less than if the iron were applied 
outside between the horseshoe magnet and the needle, or to the needle alone, the 
magnets being entirely away. On using a garnet, or a weak magnetic substance of 
any kind, I cannot find that the arrangement is at all comparable for readiness of 
indication or delicacy, with the use of a common or an astatic needle, and therefore 
I do not understand how it could become a test of the polarity of bismuth when these 
fail to show it. Still I may have made some mistake; but neither by close reference 
to the description, nor to the principles of polar action, can I discover where. 
2691. There is an experiment which Plucker described to me, and which at first 
seems to indicate strongly the polarity of bismuth. If a bar of bismuth (or phos- 
phorus) be suspended horizontally between the poles of the electro-magnet, it will 
go to the equatorial position with a certain force, passing, as I have said, from 
stronger to weaker places of action (2267.)* If a bar of iron of the same size be fixed 
in the equatorial position a little below the plane in which the diamagnetic bar is 
moving, the latter will proceed to the equatorial position with much greater force 
than before, and this is considered as due to the circumstance, that, on the side 
where the iron has N polarity, the diamagnetic body has S polarity, and that on the 
other side the S polarity of the iron and the N polarity of the bismuth also coincide. 
2692. It is however very evident that the lines of magnetic force have been altered 
sufficiently in their intensity of direction, by the presence of the iron, to account 
fully for the increased effect. For, consider the bar as just leaving the axial position 
and going to the equatorial position ; at the moment of starting its extremities are in 
places of stronger magnetic force than before, for it cannot be doubted for a moment 
that the iron bar determines more force from pole to pole of the electro-magnet than 
if it were away. On the other hand, when it has attained the equatorial position, 
the extremities are under a much weaker magnetic force than they were subject to 
in the same places before ; for the iron bar determines downwards upon itself much 
