104 Dr. Faraday's Experimental Researches in Electricity : 



ceased to fall any further. The effect of ti?ne, both in the 

 rising and falling of power, has been referred to on many 

 former occasions (2170. 2650.), and is very beautifully seen 

 here. 



2689. Returning to the subject of the assumed polarity of 

 bismuth, I may and ought to refer to an experiment made by 

 Reich, and described by Weber*, which, if 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 supposed 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 rea- 

 diness 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 phosphorus) 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.). 



* Taylor's Scientific Memoirs, vol. v. p. 480. 



