188 Dr. Tyndall on Diamagneitsm and Magneo^ystalUc Action, 



the iron ball, was laid U])on one end of the torsion -balance ; the op- 

 posite core was excited by a current of 30°, and the force neeessaiy 

 to effect a sepai-ation of the core and the sphere was determined : 

 it amounted to 20° of torsion. The same plate of glass used in 

 the last experiment was j)laccd against the core end, apd.^ie 

 force necessary to effect a separation from it with a current jpi 

 30^ was also determined. The difference, whicli in the case, of 

 the soft iron amounted to f§ths of the primitive attraction, was 

 here scarcely appreciable. At a distance of j^th of an inch the 

 sphere of sulphate of iron was almost as strongly attract6(}' AS 

 when in immediate contact. \' 



Similar experiments were made with a pellet of carbonate of 

 iron, and with the same result. At a distance of |th of an inch 

 the attraction was two-thirds of that exerted in the case of con- 

 tact. An interval of y^jVu*^^ °^ ^^^ ^^^^^ ^^ more than sufficient 

 to effect a proportionate diminution in the case of soft iron. 



A salt of iron in the immediate neighbourhood of the poles 

 behaves like iron itself at a considerable distance, and the de- 

 portment of bismuth is exactly similar. A slight change of po- 

 sition will make no great difference of attraction in the one case 

 or of repulsion in the other. To make the antithesis between 

 magnetism and diamagnetism perfect, we require a yet undisco- 

 vered metal, which shall bear the same relation to bismuth, an- 

 timony, sulphur, &c., which iron does to a salt of iron. Whe- 

 ther nature has such a metal in store for the enterprizinff phyr 

 sicist, is a problem on which I will hazard no conjecture., ' ^^ ^^ 



Principal Results of the foregoing Investigation!^^ "^^f^-i^^ 



1 . The repulsion of a diamagnetic substance placed at a fixed 

 distance from the pole of a magnet is governed hy the same daw fiS 

 the attraction of a magnetic substance. ,hHu< oifi 



2. The entire mass of a magnetic substance is most strongly at^ 

 traded when the attracting force acts parallel to that line which sets- 

 axial when the substance is suspended in the magnetic field ; and the, 

 entire mass of a diamagnetic substance is most strongly repelled 

 when the repulsion acts parallel to the line which sets equatorial in 

 the magnetic field. 



3. The superior attraction and repulsion of the mass in a par- 

 ticular direction is due to the fact, that in this direction the mate- 

 rial particles are ranged more closely together than in other direcr 

 tions ; tlie force exerted being attractive or repulsive according as 

 the particles are magnetic or diamagnetic. This is a law appli- 

 cable to matte?' in genei'al, the phanomena exhibited by crystals in 

 the magnetic field being particular manifestations of the same. 



Berlin, June 1851. 



