218 Faraday. 



this investigation, when suspended between the poles of an 

 electro-magnet, set itself across the line joining the poles : thus 

 behaving in the contrary way to a bar of an ordinary magnetic 

 substance, which would tend to set itself along this line. A 

 simpler manifestation of the effect was obtained when a cube 

 or sphere of the substance was used ; in such forms it showed 

 a disposition to move from the stronger to the weaker places 

 of the magnetic field. The pointing of the bar was then seen 

 to be merely the resultant of the tendencies of each of its 

 particles to move outwards into the positions of weakest 

 magnetic action. 



Many other bodies besides heavy glass were found to 

 display the same property ; in particular, bismuth.* The name 

 diamagnetic was given to them. 



" Theoretically," remarked Faraday, " an explanation of the 

 movements of the diamagnetic bodies might be offered in the 

 supposition that magnetic induction caused in them a contrary 

 state to that which it produced in magnetic matter ; i.e. that if 

 a particle of each kind of matter were placed in the magnetic 

 field, both would become magnetic, and each would have its 

 axis parallel to the resultant of magnetic force passing through 

 it ; but the particle of magnetic matter would have its north 

 and south poles opposite, or facing toward the contrary poles 

 of the inducing magnet, whereas with the diamagnetic particles 

 the reverse would be the case ; and hence would result approxi- 

 mation in the one substance, recession in the other. Upon 

 Ampere's theory, this view would be equivalent to the sup- 

 position that, as currents are induced in iron and magnetics 

 parallel to those existing in the inducing magnet or battery 

 wire, so in bismuth, heavy glass, and diamagnetic bodies, the 

 currents induced are in the contrary direction." 



This explanation became generally known as the " hypothesis 

 of diamagnetic polarity " ; it represents diamagnetism as similar 



* The repulsion of bismuth in the magnetic field had been previously observed 

 by A. Brugmans in 1778; Antonii Brugmans Magnetismus, Lugd. Bat., 1778. 

 t Exp. Res., 2429. 



