196 Mr. Faraday y on certain [Feb. 22, 



WEEKLY EVENING MEETING, 

 Friday, February 22. 



Sir Benjamin Collins Brodie, Bart. D.C.L. F.R.S. 



Vice-President, in the Chair. 



Mr. Faraday, D.C.L. F.R.S. 

 Ow certain Magnetic Actions and Affections. 



All bodies subject to magnetic induction, when placed in the 

 ordinary magnetic field between the poles of a magnet, are affect- 

 ed ; paramagnetic bodies tend to pass bodily from weaker to 

 stronger places of force, and diamagnetic bodies from stronger to 

 weaker places of force. If the bcwiies are elongated, then those 

 that are paramagnetic set along the lines of force, and those that 

 are diamagnetic across them : but if these bodies have a spherical 

 form, are amorphous, and are perfectly free from permanent mag- 

 netic charge, they have no tendency to set in a particular direction. 

 Nevertheless, there are bodies of both classes, which being crystal- 

 line, have the power of setting when a single crystal is wrought into 

 the form of a sphere, and these are called magne-crystals ; their 

 number is increasing continually ; carbonate of lime, bismuth, 

 tourmaline, &c., are of this nature. Bodies which being magnetic, 

 set, because they are elongated, are greatly influenced in the force of 

 the set by the nature of the medium surrounding them, and to such 

 an extent that they not merely vary in their force from the maximum 

 to nothing, but will often set axially in one medium, and equatori- 

 ally in another. Yet the same bodies, if magne-crystallic and 

 formed into spheres, though they set well in the magnetic field, will 

 set with the same force whatever the change in the media about 

 tliem, and are perfectly freed from the influence of the latter. 

 Thus, if a crystal of bismuth formed into a sphere, or a vertical cylin- 

 der, has, when suspended, its magne-crystallic axis horizontal, and 

 if the various media about it, from saturated solution of sulphate 

 of iron, up to phosphorus, through air, water, alcohol, oil, be 

 changed one for another, no alteration in the amount of torsion 

 force required to displace the magne-crystal will occur, provided 

 the force of the magnet be constant, notwithstanding that the list 

 of media includes highly paramagnetic and diamagnetic bodies ; and 

 in such cases the measurement of the power of set is relieved from 

 a multitude of interfering circumstances existing in other cases, and 

 that power which is dependent upon the internal structure and con- 



